Investments (Available For Sale Securities Continuous Unrealized Loss Position) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Schedule of Trading Securities and Other Trading Assets [Line Items]
Less than 12 Months, Fair Value	$ 1,185	$ 912
Less than 12 Months, Unrealized Losses	(21)	(36)
12 Months or Longer, Fair Value	907	1,475
12 Months or Longer, Unrealized Losses	(257)	(442)
Total, Fair Value	2,092	2,387
Total, Unrealized Losses	(278)	(478)
Fixed-Maturity Investments [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Less than 12 Months, Fair Value	1,128	820
Less than 12 Months, Unrealized Losses	(21)	(33)
12 Months or Longer, Fair Value	725	1,252
12 Months or Longer, Unrealized Losses	(226)	(385)
Total, Fair Value	1,853	2,072
Total, Unrealized Losses	(247)	(418)
Total Other Investments [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Less than 12 Months, Fair Value	45	47
Less than 12 Months, Unrealized Losses		(3)
12 Months or Longer, Fair Value		45
12 Months or Longer, Unrealized Losses		(16)
Total, Fair Value	45	92
Total, Unrealized Losses		(19)
Perpetual Preferred Securities [Member] | Total Other Investments [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Less than 12 Months, Fair Value	45	47
Less than 12 Months, Unrealized Losses		(3)
12 Months or Longer, Fair Value		45
12 Months or Longer, Unrealized Losses		(16)
Total, Fair Value	45	92
Total, Unrealized Losses		(19)
Taxable Bonds [Member] | Fixed-Maturity Investments [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Less than 12 Months, Fair Value	1,115	806
Less than 12 Months, Unrealized Losses	(21)	(33)
12 Months or Longer, Fair Value	701	1,177
12 Months or Longer, Unrealized Losses	(225)	(383)
Total, Fair Value	1,816	1,983
Total, Unrealized Losses	(246)	(416)
Taxable Bonds [Member] | U.S. Treasury And Government Agency [Member] | Fixed-Maturity Investments [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Less than 12 Months, Fair Value	587	200
Less than 12 Months, Unrealized Losses	(4)
Total, Fair Value	587	200
Total, Unrealized Losses	(4)
Taxable Bonds [Member] | Foreign Governments [Member] | Fixed-Maturity Investments [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Less than 12 Months, Fair Value	22	20
12 Months or Longer, Fair Value	1
Total, Fair Value	23	20
Taxable Bonds [Member] | Corporate Obligations [Member] | Fixed-Maturity Investments [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Less than 12 Months, Fair Value	300	297
Less than 12 Months, Unrealized Losses	(9)	(15)
12 Months or Longer, Fair Value	195	418
12 Months or Longer, Unrealized Losses	(28)	(91)
Total, Fair Value	495	715
Total, Unrealized Losses	(37)	(106)
Taxable Bonds [Member] | State And Municipal Bonds [Member] | Fixed-Maturity Investments [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Less than 12 Months, Fair Value	145	152
Less than 12 Months, Unrealized Losses	(4)	(2)
12 Months or Longer, Fair Value	70	76
12 Months or Longer, Unrealized Losses	(16)	(15)
Total, Fair Value	215	228
Total, Unrealized Losses	(20)	(17)
Tax-Exempt Bonds [Member] | State And Municipal Bonds [Member] | Fixed-Maturity Investments [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Less than 12 Months, Fair Value	13	14
12 Months or Longer, Fair Value	24	75
12 Months or Longer, Unrealized Losses	(1)	(2)
Total, Fair Value	37	89
Total, Unrealized Losses	(1)	(2)
Mortgage-Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	360
Total, Unrealized Losses	(91)
Mortgage-Backed Securities [Member] | Taxable Bonds [Member] | Residential Mortgage-Backed Securities [Member] | Fixed-Maturity Investments [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Less than 12 Months, Fair Value	13	20
12 Months or Longer, Fair Value	46	49
Total, Fair Value	59	69
Mortgage-Backed Securities [Member] | Taxable Bonds [Member] | Residential Mortgage-Backed Non-Agency [Member] | Fixed-Maturity Investments [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Less than 12 Months, Fair Value	22	34
Less than 12 Months, Unrealized Losses	(4)	(5)
12 Months or Longer, Fair Value	148	167
12 Months or Longer, Unrealized Losses	(61)	(78)
Total, Fair Value	170	201
Total, Unrealized Losses	(65)	(83)
Mortgage-Backed Securities [Member] | Taxable Bonds [Member] | Commercial Mortgage-Backed [Member] | Fixed-Maturity Investments [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Less than 12 Months, Fair Value	12	17
Less than 12 Months, Unrealized Losses		(2)
12 Months or Longer, Fair Value	24	22
12 Months or Longer, Unrealized Losses	(7)	(8)
Total, Fair Value	36	39
Total, Unrealized Losses	(7)	(10)
Asset-Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	330
Total, Unrealized Losses	125
Asset-Backed Securities [Member] | Taxable Bonds [Member] | Collateralized Debt Obligations [Member] | Fixed-Maturity Investments [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Less than 12 Months, Fair Value	8	13
Less than 12 Months, Unrealized Losses		(2)
12 Months or Longer, Fair Value	93	117
12 Months or Longer, Unrealized Losses	(94)	(116)
Total, Fair Value	101	130
Total, Unrealized Losses	(94)	(118)
Asset-Backed Securities [Member] | Taxable Bonds [Member] | Other Asset-Backed [Member] | Fixed-Maturity Investments [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Less than 12 Months, Fair Value	6	53
Less than 12 Months, Unrealized Losses		(7)
12 Months or Longer, Fair Value	124	328
12 Months or Longer, Unrealized Losses	(19)	(75)
Total, Fair Value	130	381
Total, Unrealized Losses	(19)	(82)
Variable Interest Entity [Member] | Corporate Obligations [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Less than 12 Months, Fair Value		2
Total, Fair Value		2
Variable Interest Entity [Member] | Mortgage-Backed Securities [Member] | Residential Mortgage-Backed Non-Agency [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Less than 12 Months, Fair Value	3	3
12 Months or Longer, Fair Value	92	90
12 Months or Longer, Unrealized Losses	(19)	(26)
Total, Fair Value	95	93
Total, Unrealized Losses	(19)	(26)
Variable Interest Entity [Member] | Asset-Backed Securities [Member] | Collateralized Debt Obligations [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Less than 12 Months, Fair Value	9	9
12 Months or Longer, Fair Value	90	88
12 Months or Longer, Unrealized Losses	(12)	(15)
Total, Fair Value	99	97
Total, Unrealized Losses	(12)	(15)
Variable Interest Entity [Member] | Asset-Backed Securities [Member] | Other Asset-Backed [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Less than 12 Months, Fair Value		31
Total, Fair Value		$ 31