Schedule I - Summary of Investments (Details) $ in Millions	Dec. 31, 2017 USD ($)
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	$ 27,349
Amount at which shown in the Consolidated Balance Sheet	28,619
Fixed Maturties [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	21,867
Fair value	23,138
Amount at which shown in the Consolidated Balance Sheet	23,138
United States government and government agencies and authorities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	541
Fair value	779
Amount at which shown in the Consolidated Balance Sheet	779
States, municipalities and political subdivisions [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	1,196
Fair value	1,287
Amount at which shown in the Consolidated Balance Sheet	1,287
Foreign governments [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	2,360
Fair value	2,487
Amount at which shown in the Consolidated Balance Sheet	2,487
Public utilities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	2,187
Fair value	2,342
Amount at which shown in the Consolidated Balance Sheet	2,342
All other corporate bonds [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	15,107
Fair value	15,739
Amount at which shown in the Consolidated Balance Sheet	15,739
Mortgage and other asset-backed [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	469
Fair value	497
Amount at which shown in the Consolidated Balance Sheet	497
Redeemable preferred stocks [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	7
Fair value	7
Amount at which shown in the Consolidated Balance Sheet	7
Equity securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	589
Fair value	588
Amount at which shown in the Consolidated Balance Sheet	588
Industrial, miscellaneous and all other [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	485
Fair value	496
Amount at which shown in the Consolidated Balance Sheet	496
Non-redeemable preferred stock [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	104
Fair value	92
Amount at which shown in the Consolidated Balance Sheet	92
Commercial mortgage loans on real estate [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	1,761
Amount at which shown in the Consolidated Balance Sheet	1,761
Policy loans [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	1,415
Amount at which shown in the Consolidated Balance Sheet	1,415
Other long-term investments [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	1,518
Amount at which shown in the Consolidated Balance Sheet	1,518
Short-term investments [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	199
Amount at which shown in the Consolidated Balance Sheet	$ 199