Schedule I (Details) $ in Millions	Dec. 31, 2016 USD ($)
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	$ 98,158
Fair Value	99,120
Amount at Which Shown in the Balance Sheet	99,094
Fixed maturities available for sale
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	79,536
Fair Value	80,115
Amount at Which Shown in the Balance Sheet	80,115
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	2,883
Fair Value	2,870
Amount at Which Shown in the Balance Sheet	2,870
Fixed maturities available for sale | Foreign
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	20,929
Fair Value	21,440
Amount at Which Shown in the Balance Sheet	21,440
Fixed maturities available for sale | Corporate securities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	23,736
Fair Value	24,149
Amount at Which Shown in the Balance Sheet	24,149
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	14,066
Fair Value	14,007
Amount at Which Shown in the Balance Sheet	14,007
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	17,922
Fair Value	17,649
Amount at Which Shown in the Balance Sheet	17,649
Fixed maturities held to maturity
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	10,644
Fair Value	10,670
Amount at Which Shown in the Balance Sheet	10,644
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	655
Fair Value	661
Amount at Which Shown in the Balance Sheet	655
Fixed maturities held to maturity | Foreign
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	640
Fair Value	667
Amount at Which Shown in the Balance Sheet	640
Fixed maturities held to maturity | Corporate securities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	2,771
Fair Value	2,795
Amount at Which Shown in the Balance Sheet	2,771
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	1,393
Fair Value	1,428
Amount at Which Shown in the Balance Sheet	1,393
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	5,185
Fair Value	5,119
Amount at Which Shown in the Balance Sheet	5,185
Industrial, miscellaneous, and all others
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	706
Fair Value	814
Amount at Which Shown in the Balance Sheet	814
Short-term investments
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	3,002
Fair Value	3,002
Amount at Which Shown in the Balance Sheet	3,002
Other investments
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	4,270
Fair Value	4,519
Amount at Which Shown in the Balance Sheet	$ 4,519