v3.26.1
Shareholder Report, Holdings (Details)
Apr. 30, 2026
C000111485 [Member] | NVIDIA Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000111485 [Member] | Charles Schwab Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.50%
C000111485 [Member] | Schneider Electric SE [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.50%
C000111485 [Member] | Willis Towers Watson PLC [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.20%
C000111485 [Member] | Medtronic PLC [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.10%
C000111485 [Member] | Amazon com Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.50%
C000111485 [Member] | Alphabet Inc A [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.50%
C000111485 [Member] | Visa Inc A [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.30%
C000111485 [Member] | Broadcom Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000111485 [Member] | Microsoft Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.50%
C000111485 [Member] | Other Countries [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.80%
C000111485 [Member] | JAPAN  
Holdings [Line Items]  
Percent of Total Investments 2.10%
C000111485 [Member] | FRANCE  
Holdings [Line Items]  
Percent of Total Investments 10.20%
C000111485 [Member] | SWITZERLAND  
Holdings [Line Items]  
Percent of Total Investments 4.40%
C000111485 [Member] | CANADA  
Holdings [Line Items]  
Percent of Total Investments 1.60%
C000111485 [Member] | GERMANY  
Holdings [Line Items]  
Percent of Total Investments 4.30%
C000111485 [Member] | SPAIN  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000111485 [Member] | UNITED STATES  
Holdings [Line Items]  
Percent of Total Investments 57.90%
C000111485 [Member] | TAIWAN  
Holdings [Line Items]  
Percent of Total Investments 1.40%
C000111485 [Member] | UNITED KINGDOM  
Holdings [Line Items]  
Percent of Total Investments 9.30%
C000111485 [Member] | Money Market Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.00%
C000111485 [Member] | Equity [Member]  
Holdings [Line Items]  
Percent of Total Investments 99.00%
C000006616 [Member] | NVIDIA Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006616 [Member] | Charles Schwab Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.50%
C000006616 [Member] | Schneider Electric SE [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.50%
C000006616 [Member] | Willis Towers Watson PLC [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.20%
C000006616 [Member] | Medtronic PLC [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.10%
C000006616 [Member] | Amazon com Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.50%
C000006616 [Member] | Alphabet Inc A [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.50%
C000006616 [Member] | Visa Inc A [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.30%
C000006616 [Member] | Broadcom Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006616 [Member] | Microsoft Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.50%
C000006616 [Member] | Other Countries [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.80%
C000006616 [Member] | JAPAN  
Holdings [Line Items]  
Percent of Total Investments 2.10%
C000006616 [Member] | FRANCE  
Holdings [Line Items]  
Percent of Total Investments 10.20%
C000006616 [Member] | SWITZERLAND  
Holdings [Line Items]  
Percent of Total Investments 4.40%
C000006616 [Member] | CANADA  
Holdings [Line Items]  
Percent of Total Investments 1.60%
C000006616 [Member] | GERMANY  
Holdings [Line Items]  
Percent of Total Investments 4.30%
C000006616 [Member] | SPAIN  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006616 [Member] | UNITED STATES  
Holdings [Line Items]  
Percent of Total Investments 57.90%
C000006616 [Member] | TAIWAN  
Holdings [Line Items]  
Percent of Total Investments 1.40%
C000006616 [Member] | UNITED KINGDOM  
Holdings [Line Items]  
Percent of Total Investments 9.30%
C000006616 [Member] | Money Market Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.00%
C000006616 [Member] | Equity [Member]  
Holdings [Line Items]  
Percent of Total Investments 99.00%
C000006624 [Member] | NVIDIA Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006624 [Member] | Charles Schwab Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.50%
C000006624 [Member] | Schneider Electric SE [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.50%
C000006624 [Member] | Willis Towers Watson PLC [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.20%
C000006624 [Member] | Medtronic PLC [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.10%
C000006624 [Member] | Amazon com Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.50%
C000006624 [Member] | Alphabet Inc A [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.50%
C000006624 [Member] | Visa Inc A [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.30%
C000006624 [Member] | Broadcom Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006624 [Member] | Microsoft Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.50%
C000006624 [Member] | Other Countries [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.80%
C000006624 [Member] | JAPAN  
Holdings [Line Items]  
Percent of Total Investments 2.10%
C000006624 [Member] | FRANCE  
Holdings [Line Items]  
Percent of Total Investments 10.20%
C000006624 [Member] | SWITZERLAND  
Holdings [Line Items]  
Percent of Total Investments 4.40%
C000006624 [Member] | CANADA  
Holdings [Line Items]  
Percent of Total Investments 1.60%
C000006624 [Member] | GERMANY  
Holdings [Line Items]  
Percent of Total Investments 4.30%
C000006624 [Member] | SPAIN  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006624 [Member] | UNITED STATES  
Holdings [Line Items]  
Percent of Total Investments 57.90%
C000006624 [Member] | TAIWAN  
Holdings [Line Items]  
Percent of Total Investments 1.40%
C000006624 [Member] | UNITED KINGDOM  
Holdings [Line Items]  
Percent of Total Investments 9.30%
C000006624 [Member] | Money Market Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.00%
C000006624 [Member] | Equity [Member]  
Holdings [Line Items]  
Percent of Total Investments 99.00%
C000006623 [Member] | NVIDIA Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006623 [Member] | Charles Schwab Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.50%
C000006623 [Member] | Schneider Electric SE [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.50%
C000006623 [Member] | Willis Towers Watson PLC [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.20%
C000006623 [Member] | Medtronic PLC [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.10%
C000006623 [Member] | Amazon com Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.50%
C000006623 [Member] | Alphabet Inc A [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.50%
C000006623 [Member] | Visa Inc A [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.30%
C000006623 [Member] | Broadcom Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006623 [Member] | Microsoft Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.50%
C000006623 [Member] | Other Countries [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.80%
C000006623 [Member] | JAPAN  
Holdings [Line Items]  
Percent of Total Investments 2.10%
C000006623 [Member] | FRANCE  
Holdings [Line Items]  
Percent of Total Investments 10.20%
C000006623 [Member] | SWITZERLAND  
Holdings [Line Items]  
Percent of Total Investments 4.40%
C000006623 [Member] | CANADA  
Holdings [Line Items]  
Percent of Total Investments 1.60%
C000006623 [Member] | GERMANY  
Holdings [Line Items]  
Percent of Total Investments 4.30%
C000006623 [Member] | SPAIN  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006623 [Member] | UNITED STATES  
Holdings [Line Items]  
Percent of Total Investments 57.90%
C000006623 [Member] | TAIWAN  
Holdings [Line Items]  
Percent of Total Investments 1.40%
C000006623 [Member] | UNITED KINGDOM  
Holdings [Line Items]  
Percent of Total Investments 9.30%
C000006623 [Member] | Money Market Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.00%
C000006623 [Member] | Equity [Member]  
Holdings [Line Items]  
Percent of Total Investments 99.00%
C000006618 [Member] | NVIDIA Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006618 [Member] | Charles Schwab Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.50%
C000006618 [Member] | Schneider Electric SE [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.50%
C000006618 [Member] | Willis Towers Watson PLC [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.20%
C000006618 [Member] | Medtronic PLC [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.10%
C000006618 [Member] | Amazon com Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.50%
C000006618 [Member] | Alphabet Inc A [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.50%
C000006618 [Member] | Visa Inc A [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.30%
C000006618 [Member] | Broadcom Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006618 [Member] | Microsoft Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.50%
C000006618 [Member] | Other Countries [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.80%
C000006618 [Member] | JAPAN  
Holdings [Line Items]  
Percent of Total Investments 2.10%
C000006618 [Member] | FRANCE  
Holdings [Line Items]  
Percent of Total Investments 10.20%
C000006618 [Member] | SWITZERLAND  
Holdings [Line Items]  
Percent of Total Investments 4.40%
C000006618 [Member] | CANADA  
Holdings [Line Items]  
Percent of Total Investments 1.60%
C000006618 [Member] | GERMANY  
Holdings [Line Items]  
Percent of Total Investments 4.30%
C000006618 [Member] | SPAIN  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006618 [Member] | UNITED STATES  
Holdings [Line Items]  
Percent of Total Investments 57.90%
C000006618 [Member] | TAIWAN  
Holdings [Line Items]  
Percent of Total Investments 1.40%
C000006618 [Member] | UNITED KINGDOM  
Holdings [Line Items]  
Percent of Total Investments 9.30%
C000006618 [Member] | Money Market Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.00%
C000006618 [Member] | Equity [Member]  
Holdings [Line Items]  
Percent of Total Investments 99.00%
C000006617 [Member] | NVIDIA Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006617 [Member] | Charles Schwab Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.50%
C000006617 [Member] | Schneider Electric SE [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.50%
C000006617 [Member] | Willis Towers Watson PLC [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.20%
C000006617 [Member] | Medtronic PLC [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.10%
C000006617 [Member] | Amazon com Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.50%
C000006617 [Member] | Alphabet Inc A [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.50%
C000006617 [Member] | Visa Inc A [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.30%
C000006617 [Member] | Broadcom Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006617 [Member] | Microsoft Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.50%
C000006617 [Member] | Other Countries [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.80%
C000006617 [Member] | JAPAN  
Holdings [Line Items]  
Percent of Total Investments 2.10%
C000006617 [Member] | FRANCE  
Holdings [Line Items]  
Percent of Total Investments 10.20%
C000006617 [Member] | SWITZERLAND  
Holdings [Line Items]  
Percent of Total Investments 4.40%
C000006617 [Member] | CANADA  
Holdings [Line Items]  
Percent of Total Investments 1.60%
C000006617 [Member] | GERMANY  
Holdings [Line Items]  
Percent of Total Investments 4.30%
C000006617 [Member] | SPAIN  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006617 [Member] | UNITED STATES  
Holdings [Line Items]  
Percent of Total Investments 57.90%
C000006617 [Member] | TAIWAN  
Holdings [Line Items]  
Percent of Total Investments 1.40%
C000006617 [Member] | UNITED KINGDOM  
Holdings [Line Items]  
Percent of Total Investments 9.30%
C000006617 [Member] | Money Market Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.00%
C000006617 [Member] | Equity [Member]  
Holdings [Line Items]  
Percent of Total Investments 99.00%
C000006619 [Member] | NVIDIA Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006619 [Member] | Charles Schwab Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.50%
C000006619 [Member] | Schneider Electric SE [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.50%
C000006619 [Member] | Willis Towers Watson PLC [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.20%
C000006619 [Member] | Medtronic PLC [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.10%
C000006619 [Member] | Amazon com Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.50%
C000006619 [Member] | Alphabet Inc A [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.50%
C000006619 [Member] | Visa Inc A [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.30%
C000006619 [Member] | Broadcom Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006619 [Member] | Microsoft Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.50%
C000006619 [Member] | Other Countries [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.80%
C000006619 [Member] | JAPAN  
Holdings [Line Items]  
Percent of Total Investments 2.10%
C000006619 [Member] | FRANCE  
Holdings [Line Items]  
Percent of Total Investments 10.20%
C000006619 [Member] | SWITZERLAND  
Holdings [Line Items]  
Percent of Total Investments 4.40%
C000006619 [Member] | CANADA  
Holdings [Line Items]  
Percent of Total Investments 1.60%
C000006619 [Member] | GERMANY  
Holdings [Line Items]  
Percent of Total Investments 4.30%
C000006619 [Member] | SPAIN  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006619 [Member] | UNITED STATES  
Holdings [Line Items]  
Percent of Total Investments 57.90%
C000006619 [Member] | TAIWAN  
Holdings [Line Items]  
Percent of Total Investments 1.40%
C000006619 [Member] | UNITED KINGDOM  
Holdings [Line Items]  
Percent of Total Investments 9.30%
C000006619 [Member] | Money Market Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.00%
C000006619 [Member] | Equity [Member]  
Holdings [Line Items]  
Percent of Total Investments 99.00%
C000006621 [Member] | NVIDIA Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006621 [Member] | Charles Schwab Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.50%
C000006621 [Member] | Schneider Electric SE [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.50%
C000006621 [Member] | Willis Towers Watson PLC [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.20%
C000006621 [Member] | Medtronic PLC [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.10%
C000006621 [Member] | Amazon com Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.50%
C000006621 [Member] | Alphabet Inc A [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.50%
C000006621 [Member] | Visa Inc A [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.30%
C000006621 [Member] | Broadcom Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006621 [Member] | Microsoft Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.50%
C000006621 [Member] | Other Countries [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.80%
C000006621 [Member] | JAPAN  
Holdings [Line Items]  
Percent of Total Investments 2.10%
C000006621 [Member] | FRANCE  
Holdings [Line Items]  
Percent of Total Investments 10.20%
C000006621 [Member] | SWITZERLAND  
Holdings [Line Items]  
Percent of Total Investments 4.40%
C000006621 [Member] | CANADA  
Holdings [Line Items]  
Percent of Total Investments 1.60%
C000006621 [Member] | GERMANY  
Holdings [Line Items]  
Percent of Total Investments 4.30%
C000006621 [Member] | SPAIN  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006621 [Member] | UNITED STATES  
Holdings [Line Items]  
Percent of Total Investments 57.90%
C000006621 [Member] | TAIWAN  
Holdings [Line Items]  
Percent of Total Investments 1.40%
C000006621 [Member] | UNITED KINGDOM  
Holdings [Line Items]  
Percent of Total Investments 9.30%
C000006621 [Member] | Money Market Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.00%
C000006621 [Member] | Equity [Member]  
Holdings [Line Items]  
Percent of Total Investments 99.00%
C000006615 [Member] | NVIDIA Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006615 [Member] | Charles Schwab Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.50%
C000006615 [Member] | Schneider Electric SE [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.50%
C000006615 [Member] | Willis Towers Watson PLC [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.20%
C000006615 [Member] | Medtronic PLC [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.10%
C000006615 [Member] | Amazon com Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.50%
C000006615 [Member] | Alphabet Inc A [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.50%
C000006615 [Member] | Visa Inc A [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.30%
C000006615 [Member] | Broadcom Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006615 [Member] | Microsoft Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.50%
C000006615 [Member] | Other Countries [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.80%
C000006615 [Member] | JAPAN  
Holdings [Line Items]  
Percent of Total Investments 2.10%
C000006615 [Member] | FRANCE  
Holdings [Line Items]  
Percent of Total Investments 10.20%
C000006615 [Member] | SWITZERLAND  
Holdings [Line Items]  
Percent of Total Investments 4.40%
C000006615 [Member] | CANADA  
Holdings [Line Items]  
Percent of Total Investments 1.60%
C000006615 [Member] | GERMANY  
Holdings [Line Items]  
Percent of Total Investments 4.30%
C000006615 [Member] | SPAIN  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006615 [Member] | UNITED STATES  
Holdings [Line Items]  
Percent of Total Investments 57.90%
C000006615 [Member] | TAIWAN  
Holdings [Line Items]  
Percent of Total Investments 1.40%
C000006615 [Member] | UNITED KINGDOM  
Holdings [Line Items]  
Percent of Total Investments 9.30%
C000006615 [Member] | Money Market Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.00%
C000006615 [Member] | Equity [Member]  
Holdings [Line Items]  
Percent of Total Investments 99.00%
C000006625 [Member] | Other Countries [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.90%
C000006625 [Member] | Fitch, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.70%
C000006625 [Member] | Fitch, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 11.10%
C000006625 [Member] | Fitch, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.90%
C000006625 [Member] | Fitch, D Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00%
C000006625 [Member] | Not Rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.40%
C000006625 [Member] | Moody's, Aaa Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.30%
C000006625 [Member] | Money Market Funds Quality [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.20%
C000006625 [Member] | Energy Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.40%
C000006625 [Member] | Financial Services Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.50%
C000006625 [Member] | Healthcare Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.60%
C000006625 [Member] | Real Estate Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.30%
C000006625 [Member] | Communications Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.70%
C000006625 [Member] | Consumer Discretionary Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.10%
C000006625 [Member] | Consumer Staples Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.40%
C000006625 [Member] | Industrial Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.40%
C000006625 [Member] | Information Technology Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.90%
C000006625 [Member] | Materials Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.60%
C000006625 [Member] | Utilities Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.30%
C000006625 [Member] | KOREA, REPUBLIC OF  
Holdings [Line Items]  
Percent of Total Investments 2.50%
C000006625 [Member] | ITALY  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006625 [Member] | JAPAN  
Holdings [Line Items]  
Percent of Total Investments 5.90%
C000006625 [Member] | CHINA  
Holdings [Line Items]  
Percent of Total Investments 4.30%
C000006625 [Member] | FRANCE  
Holdings [Line Items]  
Percent of Total Investments 6.70%
C000006625 [Member] | SWITZERLAND  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006625 [Member] | CANADA  
Holdings [Line Items]  
Percent of Total Investments 3.50%
C000006625 [Member] | UNITED STATES  
Holdings [Line Items]  
Percent of Total Investments 47.70%
C000006625 [Member] | UNITED KINGDOM  
Holdings [Line Items]  
Percent of Total Investments 9.50%
C000006625 [Member] | Money Market Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.20%
C000006625 [Member] | Equity [Member]  
Holdings [Line Items]  
Percent of Total Investments 60.20%
C000006625 [Member] | Federal Agencies [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.60%
C000006625 [Member] | US Government Debt Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.60%
C000006625 [Member] | Non Fixed Income [Member]  
Holdings [Line Items]  
Percent of Total Investments 60.20%
C000006625 [Member] | Fixed Income Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 36.60%
C000006627 [Member] | Other Countries [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.90%
C000006627 [Member] | Fitch, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.70%
C000006627 [Member] | Fitch, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 11.10%
C000006627 [Member] | Fitch, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.90%
C000006627 [Member] | Fitch, D Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00%
C000006627 [Member] | Not Rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.40%
C000006627 [Member] | Moody's, Aaa Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.30%
C000006627 [Member] | Money Market Funds Quality [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.20%
C000006627 [Member] | Energy Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.40%
C000006627 [Member] | Financial Services Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.50%
C000006627 [Member] | Healthcare Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.60%
C000006627 [Member] | Real Estate Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.30%
C000006627 [Member] | Communications Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.70%
C000006627 [Member] | Consumer Discretionary Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.10%
C000006627 [Member] | Consumer Staples Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.40%
C000006627 [Member] | Industrial Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.40%
C000006627 [Member] | Information Technology Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.90%
C000006627 [Member] | Materials Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.60%
C000006627 [Member] | Utilities Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.30%
C000006627 [Member] | KOREA, REPUBLIC OF  
Holdings [Line Items]  
Percent of Total Investments 2.50%
C000006627 [Member] | ITALY  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006627 [Member] | JAPAN  
Holdings [Line Items]  
Percent of Total Investments 5.90%
C000006627 [Member] | CHINA  
Holdings [Line Items]  
Percent of Total Investments 4.30%
C000006627 [Member] | FRANCE  
Holdings [Line Items]  
Percent of Total Investments 6.70%
C000006627 [Member] | SWITZERLAND  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006627 [Member] | CANADA  
Holdings [Line Items]  
Percent of Total Investments 3.50%
C000006627 [Member] | UNITED STATES  
Holdings [Line Items]  
Percent of Total Investments 47.70%
C000006627 [Member] | UNITED KINGDOM  
Holdings [Line Items]  
Percent of Total Investments 9.50%
C000006627 [Member] | Money Market Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.20%
C000006627 [Member] | Equity [Member]  
Holdings [Line Items]  
Percent of Total Investments 60.20%
C000006627 [Member] | Federal Agencies [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.60%
C000006627 [Member] | US Government Debt Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.60%
C000006627 [Member] | Non Fixed Income [Member]  
Holdings [Line Items]  
Percent of Total Investments 60.20%
C000006627 [Member] | Fixed Income Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 36.60%
C000006628 [Member] | Other Countries [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.90%
C000006628 [Member] | Fitch, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.70%
C000006628 [Member] | Fitch, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 11.10%
C000006628 [Member] | Fitch, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.90%
C000006628 [Member] | Fitch, D Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00%
C000006628 [Member] | Not Rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.40%
C000006628 [Member] | Moody's, Aaa Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.30%
C000006628 [Member] | Money Market Funds Quality [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.20%
C000006628 [Member] | Energy Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.40%
C000006628 [Member] | Financial Services Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.50%
C000006628 [Member] | Healthcare Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.60%
C000006628 [Member] | Real Estate Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.30%
C000006628 [Member] | Communications Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.70%
C000006628 [Member] | Consumer Discretionary Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.10%
C000006628 [Member] | Consumer Staples Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.40%
C000006628 [Member] | Industrial Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.40%
C000006628 [Member] | Information Technology Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.90%
C000006628 [Member] | Materials Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.60%
C000006628 [Member] | Utilities Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.30%
C000006628 [Member] | KOREA, REPUBLIC OF  
Holdings [Line Items]  
Percent of Total Investments 2.50%
C000006628 [Member] | ITALY  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006628 [Member] | JAPAN  
Holdings [Line Items]  
Percent of Total Investments 5.90%
C000006628 [Member] | CHINA  
Holdings [Line Items]  
Percent of Total Investments 4.30%
C000006628 [Member] | FRANCE  
Holdings [Line Items]  
Percent of Total Investments 6.70%
C000006628 [Member] | SWITZERLAND  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006628 [Member] | CANADA  
Holdings [Line Items]  
Percent of Total Investments 3.50%
C000006628 [Member] | UNITED STATES  
Holdings [Line Items]  
Percent of Total Investments 47.70%
C000006628 [Member] | UNITED KINGDOM  
Holdings [Line Items]  
Percent of Total Investments 9.50%
C000006628 [Member] | Money Market Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.20%
C000006628 [Member] | Equity [Member]  
Holdings [Line Items]  
Percent of Total Investments 60.20%
C000006628 [Member] | Federal Agencies [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.60%
C000006628 [Member] | US Government Debt Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.60%
C000006628 [Member] | Non Fixed Income [Member]  
Holdings [Line Items]  
Percent of Total Investments 60.20%
C000006628 [Member] | Fixed Income Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 36.60%
C000006629 [Member] | Other Countries [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.90%
C000006629 [Member] | Fitch, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.70%
C000006629 [Member] | Fitch, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 11.10%
C000006629 [Member] | Fitch, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.90%
C000006629 [Member] | Fitch, D Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00%
C000006629 [Member] | Not Rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.40%
C000006629 [Member] | Moody's, Aaa Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.30%
C000006629 [Member] | Money Market Funds Quality [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.20%
C000006629 [Member] | Energy Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.40%
C000006629 [Member] | Financial Services Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.50%
C000006629 [Member] | Healthcare Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.60%
C000006629 [Member] | Real Estate Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.30%
C000006629 [Member] | Communications Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.70%
C000006629 [Member] | Consumer Discretionary Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.10%
C000006629 [Member] | Consumer Staples Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.40%
C000006629 [Member] | Industrial Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.40%
C000006629 [Member] | Information Technology Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.90%
C000006629 [Member] | Materials Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.60%
C000006629 [Member] | Utilities Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.30%
C000006629 [Member] | KOREA, REPUBLIC OF  
Holdings [Line Items]  
Percent of Total Investments 2.50%
C000006629 [Member] | ITALY  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006629 [Member] | JAPAN  
Holdings [Line Items]  
Percent of Total Investments 5.90%
C000006629 [Member] | CHINA  
Holdings [Line Items]  
Percent of Total Investments 4.30%
C000006629 [Member] | FRANCE  
Holdings [Line Items]  
Percent of Total Investments 6.70%
C000006629 [Member] | SWITZERLAND  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006629 [Member] | CANADA  
Holdings [Line Items]  
Percent of Total Investments 3.50%
C000006629 [Member] | UNITED STATES  
Holdings [Line Items]  
Percent of Total Investments 47.70%
C000006629 [Member] | UNITED KINGDOM  
Holdings [Line Items]  
Percent of Total Investments 9.50%
C000006629 [Member] | Money Market Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.20%
C000006629 [Member] | Equity [Member]  
Holdings [Line Items]  
Percent of Total Investments 60.20%
C000006629 [Member] | Federal Agencies [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.60%
C000006629 [Member] | US Government Debt Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.60%
C000006629 [Member] | Non Fixed Income [Member]  
Holdings [Line Items]  
Percent of Total Investments 60.20%
C000006629 [Member] | Fixed Income Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 36.60%
C000006631 [Member] | Other Countries [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.90%
C000006631 [Member] | Fitch, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.70%
C000006631 [Member] | Fitch, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 11.10%
C000006631 [Member] | Fitch, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.90%
C000006631 [Member] | Fitch, D Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00%
C000006631 [Member] | Not Rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.40%
C000006631 [Member] | Moody's, Aaa Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.30%
C000006631 [Member] | Money Market Funds Quality [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.20%
C000006631 [Member] | Energy Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.40%
C000006631 [Member] | Financial Services Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.50%
C000006631 [Member] | Healthcare Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.60%
C000006631 [Member] | Real Estate Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.30%
C000006631 [Member] | Communications Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.70%
C000006631 [Member] | Consumer Discretionary Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.10%
C000006631 [Member] | Consumer Staples Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.40%
C000006631 [Member] | Industrial Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.40%
C000006631 [Member] | Information Technology Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.90%
C000006631 [Member] | Materials Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.60%
C000006631 [Member] | Utilities Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.30%
C000006631 [Member] | KOREA, REPUBLIC OF  
Holdings [Line Items]  
Percent of Total Investments 2.50%
C000006631 [Member] | ITALY  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006631 [Member] | JAPAN  
Holdings [Line Items]  
Percent of Total Investments 5.90%
C000006631 [Member] | CHINA  
Holdings [Line Items]  
Percent of Total Investments 4.30%
C000006631 [Member] | FRANCE  
Holdings [Line Items]  
Percent of Total Investments 6.70%
C000006631 [Member] | SWITZERLAND  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006631 [Member] | CANADA  
Holdings [Line Items]  
Percent of Total Investments 3.50%
C000006631 [Member] | UNITED STATES  
Holdings [Line Items]  
Percent of Total Investments 47.70%
C000006631 [Member] | UNITED KINGDOM  
Holdings [Line Items]  
Percent of Total Investments 9.50%
C000006631 [Member] | Money Market Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.20%
C000006631 [Member] | Equity [Member]  
Holdings [Line Items]  
Percent of Total Investments 60.20%
C000006631 [Member] | Federal Agencies [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.60%
C000006631 [Member] | US Government Debt Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.60%
C000006631 [Member] | Non Fixed Income [Member]  
Holdings [Line Items]  
Percent of Total Investments 60.20%
C000006631 [Member] | Fixed Income Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 36.60%
C000006633 [Member] | Other Countries [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.90%
C000006633 [Member] | Fitch, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.70%
C000006633 [Member] | Fitch, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 11.10%
C000006633 [Member] | Fitch, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.90%
C000006633 [Member] | Fitch, D Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00%
C000006633 [Member] | Not Rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.40%
C000006633 [Member] | Moody's, Aaa Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.30%
C000006633 [Member] | Money Market Funds Quality [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.20%
C000006633 [Member] | Energy Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.40%
C000006633 [Member] | Financial Services Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.50%
C000006633 [Member] | Healthcare Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.60%
C000006633 [Member] | Real Estate Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.30%
C000006633 [Member] | Communications Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.70%
C000006633 [Member] | Consumer Discretionary Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.10%
C000006633 [Member] | Consumer Staples Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.40%
C000006633 [Member] | Industrial Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.40%
C000006633 [Member] | Information Technology Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.90%
C000006633 [Member] | Materials Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.60%
C000006633 [Member] | Utilities Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.30%
C000006633 [Member] | KOREA, REPUBLIC OF  
Holdings [Line Items]  
Percent of Total Investments 2.50%
C000006633 [Member] | ITALY  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006633 [Member] | JAPAN  
Holdings [Line Items]  
Percent of Total Investments 5.90%
C000006633 [Member] | CHINA  
Holdings [Line Items]  
Percent of Total Investments 4.30%
C000006633 [Member] | FRANCE  
Holdings [Line Items]  
Percent of Total Investments 6.70%
C000006633 [Member] | SWITZERLAND  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006633 [Member] | CANADA  
Holdings [Line Items]  
Percent of Total Investments 3.50%
C000006633 [Member] | UNITED STATES  
Holdings [Line Items]  
Percent of Total Investments 47.70%
C000006633 [Member] | UNITED KINGDOM  
Holdings [Line Items]  
Percent of Total Investments 9.50%
C000006633 [Member] | Money Market Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.20%
C000006633 [Member] | Equity [Member]  
Holdings [Line Items]  
Percent of Total Investments 60.20%
C000006633 [Member] | Federal Agencies [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.60%
C000006633 [Member] | US Government Debt Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.60%
C000006633 [Member] | Non Fixed Income [Member]  
Holdings [Line Items]  
Percent of Total Investments 60.20%
C000006633 [Member] | Fixed Income Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 36.60%
C000006634 [Member] | Other Countries [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.90%
C000006634 [Member] | Fitch, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.70%
C000006634 [Member] | Fitch, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 11.10%
C000006634 [Member] | Fitch, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.90%
C000006634 [Member] | Fitch, D Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00%
C000006634 [Member] | Not Rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.40%
C000006634 [Member] | Moody's, Aaa Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.30%
C000006634 [Member] | Money Market Funds Quality [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.20%
C000006634 [Member] | Energy Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.40%
C000006634 [Member] | Financial Services Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.50%
C000006634 [Member] | Healthcare Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.60%
C000006634 [Member] | Real Estate Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.30%
C000006634 [Member] | Communications Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.70%
C000006634 [Member] | Consumer Discretionary Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.10%
C000006634 [Member] | Consumer Staples Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.40%
C000006634 [Member] | Industrial Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.40%
C000006634 [Member] | Information Technology Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.90%
C000006634 [Member] | Materials Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.60%
C000006634 [Member] | Utilities Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.30%
C000006634 [Member] | KOREA, REPUBLIC OF  
Holdings [Line Items]  
Percent of Total Investments 2.50%
C000006634 [Member] | ITALY  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006634 [Member] | JAPAN  
Holdings [Line Items]  
Percent of Total Investments 5.90%
C000006634 [Member] | CHINA  
Holdings [Line Items]  
Percent of Total Investments 4.30%
C000006634 [Member] | FRANCE  
Holdings [Line Items]  
Percent of Total Investments 6.70%
C000006634 [Member] | SWITZERLAND  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006634 [Member] | CANADA  
Holdings [Line Items]  
Percent of Total Investments 3.50%
C000006634 [Member] | UNITED STATES  
Holdings [Line Items]  
Percent of Total Investments 47.70%
C000006634 [Member] | UNITED KINGDOM  
Holdings [Line Items]  
Percent of Total Investments 9.50%
C000006634 [Member] | Money Market Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.20%
C000006634 [Member] | Equity [Member]  
Holdings [Line Items]  
Percent of Total Investments 60.20%
C000006634 [Member] | Federal Agencies [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.60%
C000006634 [Member] | US Government Debt Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.60%
C000006634 [Member] | Non Fixed Income [Member]  
Holdings [Line Items]  
Percent of Total Investments 60.20%
C000006634 [Member] | Fixed Income Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 36.60%
C000006626 [Member] | Other Countries [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.90%
C000006626 [Member] | Fitch, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.70%
C000006626 [Member] | Fitch, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 11.10%
C000006626 [Member] | Fitch, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.90%
C000006626 [Member] | Fitch, D Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00%
C000006626 [Member] | Not Rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.40%
C000006626 [Member] | Moody's, Aaa Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.30%
C000006626 [Member] | Money Market Funds Quality [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.20%
C000006626 [Member] | Energy Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.40%
C000006626 [Member] | Financial Services Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.50%
C000006626 [Member] | Healthcare Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.60%
C000006626 [Member] | Real Estate Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.30%
C000006626 [Member] | Communications Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.70%
C000006626 [Member] | Consumer Discretionary Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.10%
C000006626 [Member] | Consumer Staples Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.40%
C000006626 [Member] | Industrial Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.40%
C000006626 [Member] | Information Technology Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.90%
C000006626 [Member] | Materials Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.60%
C000006626 [Member] | Utilities Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.30%
C000006626 [Member] | KOREA, REPUBLIC OF  
Holdings [Line Items]  
Percent of Total Investments 2.50%
C000006626 [Member] | ITALY  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006626 [Member] | JAPAN  
Holdings [Line Items]  
Percent of Total Investments 5.90%
C000006626 [Member] | CHINA  
Holdings [Line Items]  
Percent of Total Investments 4.30%
C000006626 [Member] | FRANCE  
Holdings [Line Items]  
Percent of Total Investments 6.70%
C000006626 [Member] | SWITZERLAND  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000006626 [Member] | CANADA  
Holdings [Line Items]  
Percent of Total Investments 3.50%
C000006626 [Member] | UNITED STATES  
Holdings [Line Items]  
Percent of Total Investments 47.70%
C000006626 [Member] | UNITED KINGDOM  
Holdings [Line Items]  
Percent of Total Investments 9.50%
C000006626 [Member] | Money Market Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.20%
C000006626 [Member] | Equity [Member]  
Holdings [Line Items]  
Percent of Total Investments 60.20%
C000006626 [Member] | Federal Agencies [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.60%
C000006626 [Member] | US Government Debt Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.60%
C000006626 [Member] | Non Fixed Income [Member]  
Holdings [Line Items]  
Percent of Total Investments 60.20%
C000006626 [Member] | Fixed Income Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 36.60%
C000111486 [Member] | Other Countries [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.90%
C000111486 [Member] | Fitch, AA Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.70%
C000111486 [Member] | Fitch, A Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 11.10%
C000111486 [Member] | Fitch, BBB Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.90%
C000111486 [Member] | Fitch, D Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.00%
C000111486 [Member] | Not Rated [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.40%
C000111486 [Member] | Moody's, Aaa Rating [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.30%
C000111486 [Member] | Money Market Funds Quality [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.20%
C000111486 [Member] | Energy Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.40%
C000111486 [Member] | Financial Services Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.50%
C000111486 [Member] | Healthcare Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 8.60%
C000111486 [Member] | Real Estate Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.30%
C000111486 [Member] | Communications Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.70%
C000111486 [Member] | Consumer Discretionary Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.10%
C000111486 [Member] | Consumer Staples Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.40%
C000111486 [Member] | Industrial Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.40%
C000111486 [Member] | Information Technology Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.90%
C000111486 [Member] | Materials Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 2.60%
C000111486 [Member] | Utilities Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.30%
C000111486 [Member] | KOREA, REPUBLIC OF  
Holdings [Line Items]  
Percent of Total Investments 2.50%
C000111486 [Member] | ITALY  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000111486 [Member] | JAPAN  
Holdings [Line Items]  
Percent of Total Investments 5.90%
C000111486 [Member] | CHINA  
Holdings [Line Items]  
Percent of Total Investments 4.30%
C000111486 [Member] | FRANCE  
Holdings [Line Items]  
Percent of Total Investments 6.70%
C000111486 [Member] | SWITZERLAND  
Holdings [Line Items]  
Percent of Total Investments 3.00%
C000111486 [Member] | CANADA  
Holdings [Line Items]  
Percent of Total Investments 3.50%
C000111486 [Member] | UNITED STATES  
Holdings [Line Items]  
Percent of Total Investments 47.70%
C000111486 [Member] | UNITED KINGDOM  
Holdings [Line Items]  
Percent of Total Investments 9.50%
C000111486 [Member] | Money Market Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.20%
C000111486 [Member] | Equity [Member]  
Holdings [Line Items]  
Percent of Total Investments 60.20%
C000111486 [Member] | Federal Agencies [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.60%
C000111486 [Member] | US Government Debt Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.60%
C000111486 [Member] | Non Fixed Income [Member]  
Holdings [Line Items]  
Percent of Total Investments 60.20%
C000111486 [Member] | Fixed Income Securities [Member]  
Holdings [Line Items]  
Percent of Total Investments 36.60%
C000070410 [Member] | NextEra Energy Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.30%
C000070410 [Member] | Constellation Energy [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.00%
C000070410 [Member] | PG And E Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.60%
C000070410 [Member] | Xcel Energy Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.40%
C000070410 [Member] | American Electric Power Co Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.90%
C000070410 [Member] | DTE Energy Co [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.10%
C000070410 [Member] | Ameren Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.80%
C000070410 [Member] | Dominion Energy Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.80%
C000070410 [Member] | Southern Co [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.70%
C000070410 [Member] | Sempra [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.90%
C000070410 [Member] | Utilities Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 98.10%
C000070410 [Member] | Energy Renewables [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.90%
C000070410 [Member] | Money Market Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.80%
C000070410 [Member] | Equity [Member]  
Holdings [Line Items]  
Percent of Total Investments 99.20%
C000006636 [Member] | NextEra Energy Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.30%
C000006636 [Member] | Constellation Energy [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.00%
C000006636 [Member] | PG And E Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.60%
C000006636 [Member] | Xcel Energy Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.40%
C000006636 [Member] | American Electric Power Co Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.90%
C000006636 [Member] | DTE Energy Co [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.10%
C000006636 [Member] | Ameren Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.80%
C000006636 [Member] | Dominion Energy Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.80%
C000006636 [Member] | Southern Co [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.70%
C000006636 [Member] | Sempra [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.90%
C000006636 [Member] | Utilities Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 98.10%
C000006636 [Member] | Energy Renewables [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.90%
C000006636 [Member] | Money Market Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.80%
C000006636 [Member] | Equity [Member]  
Holdings [Line Items]  
Percent of Total Investments 99.20%
C000006644 [Member] | NextEra Energy Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.30%
C000006644 [Member] | Constellation Energy [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.00%
C000006644 [Member] | PG And E Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.60%
C000006644 [Member] | Xcel Energy Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.40%
C000006644 [Member] | American Electric Power Co Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.90%
C000006644 [Member] | DTE Energy Co [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.10%
C000006644 [Member] | Ameren Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.80%
C000006644 [Member] | Dominion Energy Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.80%
C000006644 [Member] | Southern Co [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.70%
C000006644 [Member] | Sempra [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.90%
C000006644 [Member] | Utilities Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 98.10%
C000006644 [Member] | Energy Renewables [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.90%
C000006644 [Member] | Money Market Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.80%
C000006644 [Member] | Equity [Member]  
Holdings [Line Items]  
Percent of Total Investments 99.20%
C000006643 [Member] | NextEra Energy Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.30%
C000006643 [Member] | Constellation Energy [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.00%
C000006643 [Member] | PG And E Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.60%
C000006643 [Member] | Xcel Energy Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.40%
C000006643 [Member] | American Electric Power Co Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.90%
C000006643 [Member] | DTE Energy Co [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.10%
C000006643 [Member] | Ameren Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.80%
C000006643 [Member] | Dominion Energy Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.80%
C000006643 [Member] | Southern Co [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.70%
C000006643 [Member] | Sempra [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.90%
C000006643 [Member] | Utilities Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 98.10%
C000006643 [Member] | Energy Renewables [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.90%
C000006643 [Member] | Money Market Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.80%
C000006643 [Member] | Equity [Member]  
Holdings [Line Items]  
Percent of Total Investments 99.20%
C000006639 [Member] | NextEra Energy Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.30%
C000006639 [Member] | Constellation Energy [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.00%
C000006639 [Member] | PG And E Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.60%
C000006639 [Member] | Xcel Energy Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.40%
C000006639 [Member] | American Electric Power Co Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.90%
C000006639 [Member] | DTE Energy Co [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.10%
C000006639 [Member] | Ameren Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.80%
C000006639 [Member] | Dominion Energy Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.80%
C000006639 [Member] | Southern Co [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.70%
C000006639 [Member] | Sempra [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.90%
C000006639 [Member] | Utilities Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 98.10%
C000006639 [Member] | Energy Renewables [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.90%
C000006639 [Member] | Money Market Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.80%
C000006639 [Member] | Equity [Member]  
Holdings [Line Items]  
Percent of Total Investments 99.20%
C000006638 [Member] | NextEra Energy Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.30%
C000006638 [Member] | Constellation Energy [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.00%
C000006638 [Member] | PG And E Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.60%
C000006638 [Member] | Xcel Energy Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.40%
C000006638 [Member] | American Electric Power Co Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.90%
C000006638 [Member] | DTE Energy Co [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.10%
C000006638 [Member] | Ameren Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.80%
C000006638 [Member] | Dominion Energy Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.80%
C000006638 [Member] | Southern Co [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.70%
C000006638 [Member] | Sempra [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.90%
C000006638 [Member] | Utilities Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 98.10%
C000006638 [Member] | Energy Renewables [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.90%
C000006638 [Member] | Money Market Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.80%
C000006638 [Member] | Equity [Member]  
Holdings [Line Items]  
Percent of Total Investments 99.20%
C000006641 [Member] | NextEra Energy Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.30%
C000006641 [Member] | Constellation Energy [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.00%
C000006641 [Member] | PG And E Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.60%
C000006641 [Member] | Xcel Energy Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.40%
C000006641 [Member] | American Electric Power Co Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.90%
C000006641 [Member] | DTE Energy Co [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.10%
C000006641 [Member] | Ameren Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.80%
C000006641 [Member] | Dominion Energy Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.80%
C000006641 [Member] | Southern Co [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.70%
C000006641 [Member] | Sempra [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.90%
C000006641 [Member] | Utilities Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 98.10%
C000006641 [Member] | Energy Renewables [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.90%
C000006641 [Member] | Money Market Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.80%
C000006641 [Member] | Equity [Member]  
Holdings [Line Items]  
Percent of Total Investments 99.20%
C000006637 [Member] | NextEra Energy Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.30%
C000006637 [Member] | Constellation Energy [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.00%
C000006637 [Member] | PG And E Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.60%
C000006637 [Member] | Xcel Energy Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.40%
C000006637 [Member] | American Electric Power Co Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.90%
C000006637 [Member] | DTE Energy Co [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.10%
C000006637 [Member] | Ameren Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.80%
C000006637 [Member] | Dominion Energy Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.80%
C000006637 [Member] | Southern Co [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.70%
C000006637 [Member] | Sempra [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.90%
C000006637 [Member] | Utilities Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 98.10%
C000006637 [Member] | Energy Renewables [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.90%
C000006637 [Member] | Money Market Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.80%
C000006637 [Member] | Equity [Member]  
Holdings [Line Items]  
Percent of Total Investments 99.20%
C000006635 [Member] | NextEra Energy Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 13.30%
C000006635 [Member] | Constellation Energy [Member]  
Holdings [Line Items]  
Percent of Total Investments 7.00%
C000006635 [Member] | PG And E Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.60%
C000006635 [Member] | Xcel Energy Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 5.40%
C000006635 [Member] | American Electric Power Co Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.90%
C000006635 [Member] | DTE Energy Co [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.10%
C000006635 [Member] | Ameren Corp [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.80%
C000006635 [Member] | Dominion Energy Inc [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.80%
C000006635 [Member] | Southern Co [Member]  
Holdings [Line Items]  
Percent of Total Investments 3.70%
C000006635 [Member] | Sempra [Member]  
Holdings [Line Items]  
Percent of Total Investments 4.90%
C000006635 [Member] | Utilities Sector [Member]  
Holdings [Line Items]  
Percent of Total Investments 98.10%
C000006635 [Member] | Energy Renewables [Member]  
Holdings [Line Items]  
Percent of Total Investments 1.90%
C000006635 [Member] | Money Market Funds [Member]  
Holdings [Line Items]  
Percent of Total Investments 0.80%
C000006635 [Member] | Equity [Member]  
Holdings [Line Items]  
Percent of Total Investments 99.20%