Consolidated Summary of Investments - Other Than Investments in Related Parties (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	$ 40,788
Fair Value	43,485
Amount at Which Shown in the Balance Sheet	43,485
Foreign Government and Government Agency Obligations [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	6,380
Fair Value	6,672
Amount at Which Shown in the Balance Sheet	6,672
Residential Mortgage-backed Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	192
Fair Value	211
Amount at Which Shown in the Balance Sheet	211
Commercial Mortgage-backed Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	1,069
Fair Value	1,090
Amount at Which Shown in the Balance Sheet	1,090
Short Term Investments [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	1,318
Fair Value	1,318
Amount at Which Shown in the Balance Sheet	1,318
Fixed Maturities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	36,958
Fair Value	38,780
Amount at Which Shown in the Balance Sheet	38,780
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	1,593
Fair Value	1,612
Amount at Which Shown in the Balance Sheet	1,612
States, Municipalities and Political Subdivisions [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	18,983
Fair Value	20,167
Amount at Which Shown in the Balance Sheet	20,167
Public Utilities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	1,065
Fair Value	1,148
Amount at Which Shown in the Balance Sheet	1,148
All Other Corporate Bonds [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	7,676
Fair Value	7,880
Amount at Which Shown in the Balance Sheet	7,880
Public Utilities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	114
Fair Value	216
Amount at Which Shown in the Balance Sheet	216
Banks, Trusts and Insurance Companies [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	101
Fair Value	185
Amount at Which Shown in the Balance Sheet	185
Industrial, Miscellaneous and Other [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	835
Fair Value	1,515
Amount at Which Shown in the Balance Sheet	1,515
Total Common Stocks [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	1,050
Fair Value	1,916
Amount at Which Shown in the Balance Sheet	1,916
Non-redeemable Preferred Stocks [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	39
Fair Value	48
Amount at Which Shown in the Balance Sheet	48
Total Equity Securities [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	1,089
Fair Value	1,964
Amount at Which Shown in the Balance Sheet	1,964
Other Invested Assets [Member]
Summary of Investments, Other than Investments in Related Parties, Reportable Data [Line Items]
Cost or Amortized Cost	1,423
Fair Value	1,423
Amount at Which Shown in the Balance Sheet	$ 1,423