Investments - Analysis of Cost or Amortized Cost, Gross Unrealized Gains and Losses and Fair Value for Investments (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	$ 8,609	$ 8,638
Gross Unrealized Gains	613	558
Gross Unrealized Losses	42	75
Fair Value	9,180	9,121
Debt Securities | States, Municipalities And Political Subdivisions
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	3,113	3,107
Gross Unrealized Gains	143	125
Gross Unrealized Losses	12	21
Fair Value	3,244	3,211
Debt Securities | Convertibles And Bonds With Warrants Attached
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	17	17
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	17	17
Debt Securities | United States Government
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	7	7
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	7	7
Debt Securities | Government-Sponsored Enterprises
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	211	227
Gross Unrealized Gains	0	0
Gross Unrealized Losses	20	27
Fair Value	191	200
Debt Securities | Foreign Government
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	10	10
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	10	10
Debt Securities | Commercial Mortgage Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	206	148
Gross Unrealized Gains	2	0
Gross Unrealized Losses	2	5
Fair Value	206	143
Debt Securities | Corporate Securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	5,045	5,122
Gross Unrealized Gains	468	433
Gross Unrealized Losses	8	22
Fair Value	5,505	5,533
Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	2,545	2,523
Gross Unrealized Gains	1,888	1,856
Gross Unrealized Losses	7	4
Fair Value	4,426	4,375
Equity Securities | Common Stock
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	2,418	2,396
Gross Unrealized Gains	1,845	1,818
Gross Unrealized Losses	6	1
Fair Value	4,257	4,213
Equity Securities | Preferred Stock
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	127	127
Gross Unrealized Gains	43	38
Gross Unrealized Losses	1	3
Fair Value	169	162
Fixed Maturities And Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	11,154	11,161
Gross Unrealized Gains	2,501	2,414
Gross Unrealized Losses	49	79
Fair Value	$ 13,606	$ 13,496