Common Stock Common Stock [Member] Entity Tax Identification Number Entity Tax Identification Number Entity File Number Entity File Number Series I Preferred Stock Series I Preferred Stock [Member] Series I Preferred Stock Cover [Abstract] Cover [Abstract] Title of 12(b) Security Title of 12(b) Security Local Phone Number Local Phone Number NEW YORK STOCK EXCHANGE, INC. NEW YORK STOCK EXCHANGE, INC. [Member] Class of Stock [Domain] Class of Stock [Domain] Soliciting Material Soliciting Material Entity Address, Address Line One Entity Address, Address Line One Entity Address, Postal Zip Code Entity Address, Postal Zip Code Entity Registrant Name Entity Registrant Name Entity Address, State or Province Entity Address, State or Province Series H Preferred Stock Series H Preferred Stock [Member] Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Written Communications Written Communications Trading Symbol Trading Symbol Exchange [Domain] Exchange [Domain] Entity Listings, Exchange [Axis] Entity Listings, Exchange [Axis] City Area Code City Area Code Document Information [Table] Document Information [Table] Document Period End Date Document Period End Date CHICAGO STOCK EXCHANGE, INC NYSE TEXAS, INC. [Member] Amendment Flag Amendment Flag Pre-commencement Issuer Tender Offer Pre-commencement Issuer Tender Offer Entity Address, City or Town Entity Address, City or Town Security Exchange Name Security Exchange Name Document Information [Line Items] Document Information [Line Items] Document Type Document Type Class of Stock [Axis] Class of Stock [Axis] Subordinated Debentures Due 2053 at 5.10 Percent Subordinated Debentures Due 2053 at 5.10 Percent [Member] Represents the subordinated debentures due in 2053 at an interest rate of 5.10 percent. Pre-commencement Tender Offer Pre-commencement Tender Offer Entity Central Index Key Entity Central Index Key Entity Emerging Growth Company Entity Emerging Growth Company Series I Preferred Stock Series J Preferred Stock [Member] Series J Preferred Stock