Schedule I (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Other investments (cost – $4,417 and $4,270)	$ 4,672	$ 4,519
Cost or Amortized Cost	100,799
Fair Value	102,497
Amount at Which Shown in the Balance Sheet	102,358
Fixed maturities available for sale
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	77,835
Fair Value	78,939
Amount at Which Shown in the Balance Sheet	78,939
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	3,701
Fair Value	3,698
Amount at Which Shown in the Balance Sheet	3,698
Fixed maturities available for sale | Foreign
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	20,514
Fair Value	21,030
Amount at Which Shown in the Balance Sheet	21,030
Fixed maturities available for sale | Corporate securities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	23,453
Fair Value	23,996
Amount at Which Shown in the Balance Sheet	23,996
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	15,279
Fair Value	15,290
Amount at Which Shown in the Balance Sheet	15,290
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	14,888
Fair Value	14,925
Amount at Which Shown in the Balance Sheet	14,925
Fixed maturities held to maturity
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	14,335
Fair Value	14,474
Amount at Which Shown in the Balance Sheet	14,335
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	908
Fair Value	915
Amount at Which Shown in the Balance Sheet	908
Fixed maturities held to maturity | Foreign
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	1,738
Fair Value	1,757
Amount at Which Shown in the Balance Sheet	1,738
Fixed maturities held to maturity | Corporate securities
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	3,159
Fair Value	3,219
Amount at Which Shown in the Balance Sheet	3,159
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	2,724
Fair Value	2,742
Amount at Which Shown in the Balance Sheet	2,724
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	5,806
Fair Value	5,841
Amount at Which Shown in the Balance Sheet	5,806
Industrial, miscellaneous, and all others
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	737
Fair Value	937
Amount at Which Shown in the Balance Sheet	937
Short-term investments
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	3,561
Fair Value	3,561
Amount at Which Shown in the Balance Sheet	3,561
Other investments
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	4,331
Fair Value	4,586
Amount at Which Shown in the Balance Sheet	4,586
All Related Party [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Other investments (cost – $4,417 and $4,270)	$ 86