Schedule I (Details) $ in Millions	Dec. 31, 2015 USD ($)
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	$ 65,459
Fair Value	66,373
Amount at Which Shown in the Balance Sheet	66,251
Fixed maturities available for sale
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	43,149
Fair Value	43,587
Amount at Which Shown in the Balance Sheet	43,587
Fixed maturities available for sale | U.S. Treasury and agency
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	2,481
Fair Value	2,528
Amount at Which Shown in the Balance Sheet	2,528
Fixed maturities available for sale | Foreign
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	13,190
Fair Value	13,445
Amount at Which Shown in the Balance Sheet	13,445
Fixed maturities available for sale | Corporate securities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	15,028
Fair Value	14,929
Amount at Which Shown in the Balance Sheet	14,929
Fixed maturities available for sale | Mortgage backed-securities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	9,827
Fair Value	9,958
Amount at Which Shown in the Balance Sheet	9,958
Fixed maturities available for sale | States, municipalities, and political subdivisions
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	2,623
Fair Value	2,727
Amount at Which Shown in the Balance Sheet	2,727
Fixed maturities held to maturity
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	8,430
Fair Value	8,552
Amount at Which Shown in the Balance Sheet	8,430
Fixed maturities held to maturity | U.S. Treasury and agency
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	733
Fair Value	745
Amount at Which Shown in the Balance Sheet	733
Fixed maturities held to maturity | Foreign
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	763
Fair Value	785
Amount at Which Shown in the Balance Sheet	763
Fixed maturities held to maturity | Corporate securities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	3,054
Fair Value	3,056
Amount at Which Shown in the Balance Sheet	3,054
Fixed maturities held to maturity | Mortgage backed-securities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	1,707
Fair Value	1,743
Amount at Which Shown in the Balance Sheet	1,707
Fixed maturities held to maturity | States, municipalities, and political subdivisions
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	2,173
Fair Value	2,223
Amount at Which Shown in the Balance Sheet	2,173
Industrial, miscellaneous, and all others
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	441
Fair Value	497
Amount at Which Shown in the Balance Sheet	497
Short-term investments
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	10,446
Fair Value	10,446
Amount at Which Shown in the Balance Sheet	10,446
Other investments
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	2,993
Fair Value	3,291
Amount at Which Shown in the Balance Sheet	$ 3,291