Investments (Available For Sale Securities Continuous Unrealized Loss Position) (Detail) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 823	$ 912
Less than 12 Months, Unrealized Losses	(5)	(36)
12 Months or Longer, Fair Value	735	1,475
12 Months or Longer, Unrealized Losses	(221)	(442)
Total, Fair Value	1,558	2,387
Total, Unrealized Losses	(226)	(478)
Fixed-Maturity Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	772	820
Less than 12 Months, Unrealized Losses	(4)	(33)
12 Months or Longer, Fair Value	500	1,252
12 Months or Longer, Unrealized Losses	(181)	(385)
Total, Fair Value	1,272	2,072
Total, Unrealized Losses	(185)	(418)
Perpetual Preferred Securities [Member] | Total Other Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	46	47
Less than 12 Months, Unrealized Losses	(1)	(3)
12 Months or Longer, Fair Value	1	45
12 Months or Longer, Unrealized Losses		(16)
Total, Fair Value	47	92
Total, Unrealized Losses	(1)	(19)
Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Fair Value	284
Total, Unrealized Losses	(63)
Asset-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total, Fair Value	288
Total, Unrealized Losses	(119)
Taxable Bonds [Member] | Fixed-Maturity Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	755	806
Less than 12 Months, Unrealized Losses	(4)	(33)
12 Months or Longer, Fair Value	477	1,177
12 Months or Longer, Unrealized Losses	(180)	(383)
Total, Fair Value	1,232	1,983
Total, Unrealized Losses	(184)	(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	471	200
Total, Fair Value	471	200
Taxable Bonds [Member] | Foreign Governments [Member] | Fixed-Maturity Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	40	20
Total, Fair Value	40	20
Taxable Bonds [Member] | Corporate Obligations [Member] | Fixed-Maturity Investments [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	211	297
Less than 12 Months, Unrealized Losses	(2)	(15)
12 Months or Longer, Fair Value	41	418
12 Months or Longer, Unrealized Losses	(22)	(91)
Total, Fair Value	252	715
Total, Unrealized Losses	(24)	(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	7	152
Less than 12 Months, Unrealized Losses		(2)
12 Months or Longer, Fair Value	76	76
12 Months or Longer, Unrealized Losses	(11)	(15)
Total, Fair Value	83	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	3	20
12 Months or Longer, Fair Value	43	49
Total, Fair Value	46	69
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	7	34
Less than 12 Months, Unrealized Losses	(1)	(5)
12 Months or Longer, Fair Value	113	167
12 Months or Longer, Unrealized Losses	(38)	(78)
Total, Fair Value	120	201
Total, Unrealized Losses	(39)	(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	5	17
Less than 12 Months, Unrealized Losses		(2)
12 Months or Longer, Fair Value	26	22
12 Months or Longer, Unrealized Losses	(5)	(8)
Total, Fair Value	31	39
Total, Unrealized Losses	(5)	(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	7	13
Less than 12 Months, Unrealized Losses	(1)	(2)
12 Months or Longer, Fair Value	87	117
12 Months or Longer, Unrealized Losses	(85)	(116)
Total, Fair Value	94	130
Total, Unrealized Losses	(86)	(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	4	53
Less than 12 Months, Unrealized Losses		(7)
12 Months or Longer, Fair Value	91	328
12 Months or Longer, Unrealized Losses	(19)	(75)
Total, Fair Value	95	381
Total, Unrealized Losses	(19)	(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	17	14
12 Months or Longer, Fair Value	23	75
12 Months or Longer, Unrealized Losses	(1)	(2)
Total, Fair Value	40	89
Total, Unrealized Losses	(1)	(2)
Variable Interest Entity [Member] | Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value		2
12 Months or Longer, Fair Value	53
12 Months or Longer, Unrealized Losses	(7)
Total, Fair Value	53	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
12 Months or Longer, Fair Value	87	90
12 Months or Longer, Unrealized Losses	(19)	(26)
Total, Fair Value	87	93
Total, Unrealized Losses	(19)	(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	5	9
12 Months or Longer, Fair Value	90	88
12 Months or Longer, Unrealized Losses	(14)	(15)
Total, Fair Value	95	97
Total, Unrealized Losses	(14)	(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
12 Months or Longer, Fair Value	4
Total, Fair Value	$ 4	$ 31