Fair Value - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets of discontinued operations		$ 32
Liabilities of discontinued operations		(8)
Corporate and Other Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	18,886	20,862
States, Municipalities and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	12,740	11,557
Residential Mortgage-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	5,233	4,971
Commercial Mortgage-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	2,144	2,063
Other Asset-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	1,235	955
Total Asset-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	8,612	7,989
U.S. Treasury and Obligations of Government-Sponsored Enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	31	144
Foreign Government [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	454	543
Redeemable Preferred Stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	42	102
Total Fixed Maturities Available-for-Sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	40,765	41,197
Fixed Maturities, Trading [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	120	123
Fixed Maturity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	40,885	41,320
Total Equity Securities Available-for-Sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	222	185
Equity Securities, Trading [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	506	686
Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	728	871
Short Term Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	5,952	6,697
Other Invested Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	143	54
Receivables [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	9	3
Life Settlement Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	82	88
Separate Account Business [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis		181
Payable to Brokers [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of liabilities, measured on a recurring basis	(552)	(44)
Level 1 [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets of discontinued operations		28
Level 1 [Member] | Corporate and Other Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	32	33
Level 1 [Member] | U.S. Treasury and Obligations of Government-Sponsored Enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	28	116
Level 1 [Member] | Foreign Government [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	41	81
Level 1 [Member] | Redeemable Preferred Stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	30	45
Level 1 [Member] | Total Fixed Maturities Available-for-Sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	131	275
Level 1 [Member] | Fixed Maturity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	131	275
Level 1 [Member] | Total Equity Securities Available-for-Sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	145	126
Level 1 [Member] | Equity Securities, Trading [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	505	678
Level 1 [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	650	804
Level 1 [Member] | Short Term Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	4,989	6,134
Level 1 [Member] | Other Invested Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	102
Level 1 [Member] | Receivables [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	2
Level 1 [Member] | Separate Account Business [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis		9
Level 1 [Member] | Payable to Brokers [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of liabilities, measured on a recurring basis	(546)	(40)
Level 2 [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets of discontinued operations		2
Liabilities of discontinued operations		(6)
Level 2 [Member] | Corporate and Other Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	18,692	20,625
Level 2 [Member] | States, Municipalities and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	12,646	11,486
Level 2 [Member] | Residential Mortgage-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	5,044	4,640
Level 2 [Member] | Commercial Mortgage-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	2,061	1,912
Level 2 [Member] | Other Asset-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	580	509
Level 2 [Member] | Total Asset-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	7,685	7,061
Level 2 [Member] | U.S. Treasury and Obligations of Government-Sponsored Enterprises [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	3	28
Level 2 [Member] | Foreign Government [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	413	462
Level 2 [Member] | Redeemable Preferred Stock [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	12	57
Level 2 [Member] | Total Fixed Maturities Available-for-Sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	39,451	39,719
Level 2 [Member] | Fixed Maturities, Trading [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	30	43
Level 2 [Member] | Fixed Maturity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	39,481	39,762
Level 2 [Member] | Total Equity Securities Available-for-Sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	61	48
Level 2 [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	61	48
Level 2 [Member] | Short Term Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	963	563
Level 2 [Member] | Other Invested Assets [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	41	54
Level 2 [Member] | Receivables [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	7	3
Level 2 [Member] | Separate Account Business [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis		171
Level 2 [Member] | Payable to Brokers [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of liabilities, measured on a recurring basis	(6)	(1)
Level 3 [Member] | Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets of discontinued operations		2
Liabilities of discontinued operations		(2)
Level 3 [Member] | Corporate and Other Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	162	204
Level 3 [Member] | States, Municipalities and Political Subdivisions [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	94	71
Level 3 [Member] | Residential Mortgage-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	189	331
Level 3 [Member] | Commercial Mortgage-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	83	151
Level 3 [Member] | Other Asset-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	655	446
Level 3 [Member] | Total Asset-Backed [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	927	928
Level 3 [Member] | Total Fixed Maturities Available-for-Sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	1,183	1,203
Level 3 [Member] | Fixed Maturities, Trading [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	90	80
Level 3 [Member] | Fixed Maturity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	1,273	1,283
Level 3 [Member] | Total Equity Securities Available-for-Sale [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	16	11
Level 3 [Member] | Equity Securities, Trading [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	1	8
Level 3 [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	17	19
Level 3 [Member] | Life Settlement Contracts [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis	82	88
Level 3 [Member] | Separate Account Business [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of assets, measured on a recurring basis		1
Level 3 [Member] | Payable to Brokers [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value of liabilities, measured on a recurring basis		$ (3)