Schedule I Summary of Investments - Other than Investments in Related Parties (Details) $ in Millions	Dec. 31, 2017 USD ($)
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	$ 309,140
Fair Value	323,959
Amount at which shown in the Balance Sheet	323,214
Fixed maturity securities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	238,233
Fair Value	251,764
Amount at which shown in the Balance Sheet	251,764
U.S. government and government sponsored entities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	5,334
Fair Value	5,458
Amount at which shown in the Balance Sheet	5,458
Obligations of states, municipalities and political subdivisions
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	17,377
Fair Value	18,644
Amount at which shown in the Balance Sheet	18,644
Non-U.S. government
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	15,116
Fair Value	15,716
Amount at which shown in the Balance Sheet	15,716
Public utilities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	17,654
Fair Value	18,870
Amount at which shown in the Balance Sheet	18,870
All other corporate and debt securities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	110,565
Fair Value	117,215
Amount at which shown in the Balance Sheet	117,215
Mortgage-backed, asset-backed and collateralized
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	72,187
Fair Value	75,861
Amount at which shown in the Balance Sheet	75,861
Equity securities and mutual funds
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	1,894
Fair Value	2,297
Amount at which shown in the Balance Sheet	2,297
Common Stock
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	1,251
Fair Value	1,610
Amount at which shown in the Balance Sheet	1,610
Public utilities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	1
Fair Value	1
Amount at which shown in the Balance Sheet	1
Banks, trust and insurance companies
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	924
Fair Value	1,126
Amount at which shown in the Balance Sheet	1,126
Industrial, miscellaneous and all other
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	326
Fair Value	483
Amount at which shown in the Balance Sheet	483
Preferred stock
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	504
Fair Value	533
Amount at which shown in the Balance Sheet	533
Mutual funds
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	139
Fair Value	154
Amount at which shown in the Balance Sheet	154
Mortgage and other loans receivable, net of allowance
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	37,023
Fair Value	37,766
Amount at which shown in the Balance Sheet	37,023
Other invested assets
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	20,682
Fair Value	20,824
Amount at which shown in the Balance Sheet	20,822
Short-term investments, at cost
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	10,386
Fair Value	10,386
Amount at which shown in the Balance Sheet	10,386
Derivative assets
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost	922
Fair Value	922
Amount at which shown in the Balance Sheet	$ 922