Schedule I - Summary of Investments (Details) $ in Millions	Dec. 31, 2015 USD ($)
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	$ 23,714
Amount at which shown in the Consolidated Balance Sheet	24,713
Debt Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	18,456
Fair value	19,455
Amount at which shown in the Consolidated Balance Sheet	19,455
Federal government and agency [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	528
Fair value	779
Amount at which shown in the Consolidated Balance Sheet	779
State and local government [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	1,496
Fair value	1,641
Amount at which shown in the Consolidated Balance Sheet	1,641
Foreign Government Debt [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	1,870
Fair value	2,014
Amount at which shown in the Consolidated Balance Sheet	2,014
Public Utility, Bonds [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	1,648
Fair value	1,743
Amount at which shown in the Consolidated Balance Sheet	1,743
All Other Corporate Bonds [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	12,364
Fair value	12,695
Amount at which shown in the Consolidated Balance Sheet	12,695
Federal agency mortgage-backed [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	48
Fair value	49
Amount at which shown in the Consolidated Balance Sheet	49
Other asset and mortgage-backed securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	492
Fair value	524
Amount at which shown in the Consolidated Balance Sheet	524
Mandatorily Redeemable Preferred Stock [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	10
Fair value	10
Amount at which shown in the Consolidated Balance Sheet	10
Equity Securities, Investment Summary [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	190
Fair value	190
Amount at which shown in the Consolidated Balance Sheet	190
Industrial, Miscellaneous, and All Others [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	91
Fair value	97
Amount at which shown in the Consolidated Balance Sheet	97
Nonredeemable Preferred Stock [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	99
Fair value	93
Amount at which shown in the Consolidated Balance Sheet	93
Mortgage Loans on Real Estate [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	1,864
Amount at which shown in the Consolidated Balance Sheet	1,864
Policy Loans [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	1,419
Amount at which shown in the Consolidated Balance Sheet	1,419
Other Long Term Investments [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	1,404
Amount at which shown in the Consolidated Balance Sheet	1,404
Short-term Investments [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	381
Amount at which shown in the Consolidated Balance Sheet	$ 381