Investments - Analysis of Cost or Amortized Cost, Gross Unrealized Gains and Losses and Fair Value for Investments (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Debt Securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	$ 8,719	$ 8,638
Gross Unrealized Gains	686	558
Gross Unrealized Losses	22	75
Fair Value	9,383	9,121
Debt Securities | States, Municipalities And Political Subdivisions
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	3,205	3,107
Gross Unrealized Gains	170	125
Gross Unrealized Losses	5	21
Fair Value	3,370	3,211
Debt Securities | Convertibles And Bonds With Warrants Attached
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	7	17
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	7	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	221	227
Gross Unrealized Gains	0	0
Gross Unrealized Losses	13	27
Fair Value	208	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	220	148
Gross Unrealized Gains	7	0
Gross Unrealized Losses	1	5
Fair Value	226	143
Debt Securities | Corporate Securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	5,049	5,122
Gross Unrealized Gains	509	433
Gross Unrealized Losses	3	22
Fair Value	5,555	5,533
Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	2,582	2,523
Gross Unrealized Gains	2,027	1,856
Gross Unrealized Losses	4	4
Fair Value	4,605	4,375
Equity Securities | Common Stock
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	2,458	2,396
Gross Unrealized Gains	1,992	1,818
Gross Unrealized Losses	3	1
Fair Value	4,447	4,213
Equity Securities | Preferred Stock
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	124	127
Gross Unrealized Gains	35	38
Gross Unrealized Losses	1	3
Fair Value	158	162
Fixed Maturities And Equity Securities
Schedule of Available-for-sale Securities [Line Items]
Cost or Amortized Cost	11,301	11,161
Gross Unrealized Gains	2,713	2,414
Gross Unrealized Losses	26	79
Fair Value	$ 13,988	$ 13,496