Investments (Available-For-Sale Securities Continuous Unrealized Loss Position) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 304	$ 912
Less than 12 Months, Unrealized Losses	(1)	(36)
12 Months or Longer, Fair Value	721	1,475
12 Months or Longer, Unrealized Losses	(190)	(442)
Total, Fair Value	1,025	2,387
Total, Unrealized Losses	(191)	(478)
Fixed-Maturity Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	304	820
Less than 12 Months, Unrealized Losses	(1)	(33)
12 Months or Longer, Fair Value	478	1,252
12 Months or Longer, Unrealized Losses	(160)	(385)
Total, Fair Value	782	2,072
Total, Unrealized Losses	(161)	(418)
Perpetual Preferred Securities [Member] | Other Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value		47
Less than 12 Months, Unrealized Losses		(3)
12 Months or Longer, Fair Value	3	45
12 Months or Longer, Unrealized Losses		(16)
Total, Fair Value	3	92
Total, Unrealized Losses		(19)
Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Fair Value	270
Total, Unrealized Losses	(52)
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Fair Value	273
Total, Unrealized Losses	(99)
Taxable Bonds [Member] | Fixed-Maturity Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	303	806
Less than 12 Months, Unrealized Losses	(1)	(33)
12 Months or Longer, Fair Value	456	1,177
12 Months or Longer, Unrealized Losses	(160)	(383)
Total, Fair Value	759	1,983
Total, Unrealized Losses	(161)	(416)
Taxable Bonds [Member] | U.S. Treasury And Government Agency [Member] | Fixed-Maturity Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	197	200
Less than 12 Months, Unrealized Losses	(1)
12 Months or Longer, Fair Value
12 Months or Longer, Unrealized Losses
Total, Fair Value	197	200
Total, Unrealized Losses	(1)
Taxable Bonds [Member] | Foreign Governments [Member] | Fixed-Maturity Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	24	20
Less than 12 Months, Unrealized Losses
12 Months or Longer, Fair Value
12 Months or Longer, Unrealized Losses
Total, Fair Value	24	20
Total, Unrealized Losses
Taxable Bonds [Member] | Corporate Obligations [Member] | Fixed-Maturity Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	60	297
Less than 12 Months, Unrealized Losses		(15)
12 Months or Longer, Fair Value	49	418
12 Months or Longer, Unrealized Losses	(21)	(91)
Total, Fair Value	109	715
Total, Unrealized Losses	(21)	(106)
Taxable Bonds [Member] | State And Municipal Bonds [Member] | Fixed-Maturity Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	6	152
Less than 12 Months, Unrealized Losses		(2)
12 Months or Longer, Fair Value	66	76
12 Months or Longer, Unrealized Losses	(11)	(15)
Total, Fair Value	72	228
Total, Unrealized Losses	(11)	(17)
Taxable Bonds [Member] | Mortgage-Backed Securities [Member] | Residential Mortgage-Backed Agency [Member] | Fixed-Maturity Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	8	20
Less than 12 Months, Unrealized Losses
12 Months or Longer, Fair Value	41	49
12 Months or Longer, Unrealized Losses
Total, Fair Value	49	69
Total, Unrealized Losses
Taxable Bonds [Member] | Mortgage-Backed Securities [Member] | Residential Mortgage-Backed Non-Agency [Member] | Fixed-Maturity Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	2	34
Less than 12 Months, Unrealized Losses		(5)
12 Months or Longer, Fair Value	102	167
12 Months or Longer, Unrealized Losses	(36)	(78)
Total, Fair Value	104	201
Total, Unrealized Losses	(36)	(83)
Taxable Bonds [Member] | Mortgage-Backed Securities [Member] | Commercial Mortgage-Backed [Member] | Fixed-Maturity Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	3	17
Less than 12 Months, Unrealized Losses		(2)
12 Months or Longer, Fair Value	27	22
12 Months or Longer, Unrealized Losses	(4)	(8)
Total, Fair Value	30	39
Total, Unrealized Losses	(4)	(10)
Taxable Bonds [Member] | Asset-Backed Securities [Member] | Collateralized Debt Obligations [Member] | Fixed-Maturity Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	2	13
Less than 12 Months, Unrealized Losses		(2)
12 Months or Longer, Fair Value	83	117
12 Months or Longer, Unrealized Losses	(74)	(116)
Total, Fair Value	85	130
Total, Unrealized Losses	(74)	(118)
Taxable Bonds [Member] | Asset-Backed Securities [Member] | Other Asset-Backed [Member] | Fixed-Maturity Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	1	53
Less than 12 Months, Unrealized Losses		(7)
12 Months or Longer, Fair Value	88	328
12 Months or Longer, Unrealized Losses	(14)	(75)
Total, Fair Value	89	381
Total, Unrealized Losses	(14)	(82)
Tax-Exempt Bonds [Member] | State And Municipal Bonds [Member] | Fixed-Maturity Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	1	14
Less than 12 Months, Unrealized Losses
12 Months or Longer, Fair Value	22	75
12 Months or Longer, Unrealized Losses		(2)
Total, Fair Value	23	89
Total, Unrealized Losses		(2)
Variable Interest Entity [Member] | Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value		2
Less than 12 Months, Unrealized Losses
12 Months or Longer, Fair Value	54
12 Months or Longer, Unrealized Losses	(7)
Total, Fair Value	54	2
Total, Unrealized Losses	(7)
Variable Interest Entity [Member] | Mortgage-Backed Securities [Member] | Residential Mortgage-Backed Non-Agency [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value		3
Less than 12 Months, Unrealized Losses
12 Months or Longer, Fair Value	87	90
12 Months or Longer, Unrealized Losses	(12)	(26)
Total, Fair Value	87	93
Total, Unrealized Losses	(12)	(26)
Variable Interest Entity [Member] | Asset-Backed Securities [Member] | Collateralized Debt Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value		9
Less than 12 Months, Unrealized Losses
12 Months or Longer, Fair Value	96	88
12 Months or Longer, Unrealized Losses	(11)	(15)
Total, Fair Value	96	97
Total, Unrealized Losses	(11)	(15)
Variable Interest Entity [Member] | Asset-Backed Securities [Member] | Other Asset-Backed [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value		31
Less than 12 Months, Unrealized Losses
12 Months or Longer, Fair Value	3
12 Months or Longer, Unrealized Losses
Total, Fair Value	3	31
Total, Unrealized Losses