Soliciting Material Soliciting Material Written Communications Written Communications Local Phone Number Local Phone Number Amendment Flag Amendment Flag Entity Emerging Growth Company Entity Emerging Growth Company Entity File Number Entity File Number Security Exchange Name Security Exchange Name 5.100% Subordinated Debentures due 2059 Subordinated Debentures Due 2059, 5.10% [Member] Subordinated Debentures Due 2059, 5.10% [Member] Debt Instrument [Axis] Debt Instrument [Axis] Entity Address, State or Province Entity Address, State or Province Entity Address, Address Line One Entity Address, Address Line One City Area Code City Area Code 4.250% Subordinated Debentures due 2060 Subordinated Debentures Due 2060, 4.25% [Member] Subordinated Debentures Due 2060, 4.25% 4.125% Subordinated Debentures due 2061 Subordinated Debentures Due 2061, 4.125% [Member] Subordinated Debentures Due 2061, 4.125% Cover [Abstract] Cover [Abstract] Entity Information [Line Items] Entity Information [Line Items] Document Period End Date Document Period End Date Pre-commencement Tender Offer Pre-commencement Tender Offer Entity Central Index Key Entity Central Index Key Pre-commencement Issuer Tender Offer Pre-commencement Issuer Tender Offer Entity Tax Identification Number Entity Tax Identification Number Entities [Table] Entities [Table] Entity Registrant Name Entity Registrant Name Trading Symbol Trading Symbol Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] 5.75% Subordinated Debentures due 2056 Subordinated Debentures Due 2056, 5.75% [Member] Subordinated Debentures Due 2056, 5.75% [Member] Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Title of 12(b) Security Title of 12(b) Security Entity Address, Postal Zip Code Entity Address, Postal Zip Code Entity Address, City or Town Entity Address, City or Town Document Type Document Type 5.700% Subordinated Debentures due 2058 Subordinated Debentures Due 2058, 5.70% [Member] Subordinated Debentures Due 2058, 5.70% [Member]