Consolidated Summary of Investments - Other Than Investments in Related Parties (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	$ 41,124
Fair Value	44,221
Amount at Which Shown in the Balance Sheet	44,221
Short term investments [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	2,528
Fair Value	2,528
Amount at Which Shown in the Balance Sheet	2,528
Fixed maturities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	35,398
Fair Value	38,076
Amount at Which Shown in the Balance Sheet	38,076
United States Government and government agencies and authorities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	902
Fair Value	964
Amount at Which Shown in the Balance Sheet	964
States, municipalities and political subdivisions [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	18,790
Fair Value	20,322
Amount at Which Shown in the Balance Sheet	20,322
Foreign government and government agency obligations [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	6,614
Fair Value	7,008
Amount at Which Shown in the Balance Sheet	7,008
Public utilities, Bonds [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	1,090
Fair Value	1,241
Amount at Which Shown in the Balance Sheet	1,241
All other corporate bonds [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	8,002
Fair Value	8,541
Amount at Which Shown in the Balance Sheet	8,541
Public utilities, Equities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	94
Fair Value	133
Amount at Which Shown in the Balance Sheet	133
Banks, Trust and Insurance, Equities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	286
Fair Value	342
Amount at Which Shown in the Balance Sheet	342
Industrial, miscellaneous and other [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	855
Fair Value	1,172
Amount at Which Shown in the Balance Sheet	1,172
Common stocks [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	1,235
Fair Value	1,647
Amount at Which Shown in the Balance Sheet	1,647
Non-redeemable preferred stocks [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	9
Fair Value	16
Amount at Which Shown in the Balance Sheet	16
Equity securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	1,244
Fair Value	1,663
Amount at Which Shown in the Balance Sheet	1,663
Other invested assets [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	1,954
Fair Value	1,954
Amount at Which Shown in the Balance Sheet	$ 1,954