Investments (Available-For-Sale Securities Continuous Unrealized Loss Position) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Schedule of Trading Securities and Other Trading Assets [Line Items]
Less than 12 Months, Fair Value	$ 912	$ 4,530
Less than 12 Months, Unrealized Losses	(36)	(142)
12 Months or Longer, Fair Value	1,475	2,424
12 Months or Longer, Unrealized Losses	(442)	(662)
Total, Fair Value	2,387	6,954
Total, Unrealized Losses	(478)	(804)
Fixed-Maturity Investments [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Less than 12 Months, Fair Value	820	4,438
Less than 12 Months, Unrealized Losses	(33)	(141)
12 Months or Longer, Fair Value	1,252	2,279
12 Months or Longer, Unrealized Losses	(385)	(650)
Total, Fair Value	2,072	6,717
Total, Unrealized Losses	(418)	(791)
Other Long Term Investments [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Less than 12 Months, Fair Value	47	23
Less than 12 Months, Unrealized Losses	(3)
12 Months or Longer, Fair Value	45	140
12 Months or Longer, Unrealized Losses	(16)	(12)
Total, Fair Value	92	163
Total, Unrealized Losses	(19)	(12)
Perpetual Preferred Securities [Member] | Other Long Term Investments [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Less than 12 Months, Fair Value	47	20
Less than 12 Months, Unrealized Losses	(3)
12 Months or Longer, Fair Value	45	140
12 Months or Longer, Unrealized Losses	(16)	(12)
Total, Fair Value	92	160
Total, Unrealized Losses	(19)	(12)
Other Long Term Investments [Member] | Other Long Term Investments [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Less than 12 Months, Fair Value		3
Total, Fair Value		3
Taxable Bonds [Member] | Fixed-Maturity Investments [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Less than 12 Months, Fair Value	806	2,436
Less than 12 Months, Unrealized Losses	(33)	(58)
12 Months or Longer, Fair Value	1,177	2,098
12 Months or Longer, Unrealized Losses	(383)	(629)
Total, Fair Value	1,983	4,534
Total, Unrealized Losses	(416)	(687)
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	200	370
Less than 12 Months, Unrealized Losses		(3)
Total, Fair Value	200	370
Total, Unrealized Losses		(3)
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	20	33
Less than 12 Months, Unrealized Losses		(1)
Total, Fair Value	20	33
Total, Unrealized Losses		(1)
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	297	685
Less than 12 Months, Unrealized Losses	(15)	(13)
12 Months or Longer, Fair Value	418	725
12 Months or Longer, Unrealized Losses	(91)	(114)
Total, Fair Value	715	1,410
Total, Unrealized Losses	(106)	(127)
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	152	437
Less than 12 Months, Unrealized Losses	(2)	(26)
12 Months or Longer, Fair Value	76	135
12 Months or Longer, Unrealized Losses	(15)	(26)
Total, Fair Value	228	572
Total, Unrealized Losses	(17)	(52)
Tax-Exempt Bonds [Member] | Fixed-Maturity Investments [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Less than 12 Months, Fair Value	14	2,002
Less than 12 Months, Unrealized Losses		(83)
12 Months or Longer, Fair Value	75	181
12 Months or Longer, Unrealized Losses	(2)	(21)
Total, Fair Value	89	2,183
Total, Unrealized Losses	(2)	(104)
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	14	2,002
Less than 12 Months, Unrealized Losses		(83)
12 Months or Longer, Fair Value	75	181
12 Months or Longer, Unrealized Losses	(2)	(21)
Total, Fair Value	89	2,183
Total, Unrealized Losses	(2)	(104)
Mortgage-Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	401
Total, Unrealized Losses	(119)
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	20	785
Less than 12 Months, Unrealized Losses		(11)
12 Months or Longer, Fair Value	49	59
12 Months or Longer, Unrealized Losses		(2)
Total, Fair Value	69	844
Total, Unrealized Losses		(13)
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	34	51
Less than 12 Months, Unrealized Losses	(5)	(2)
12 Months or Longer, Fair Value	167	336
12 Months or Longer, Unrealized Losses	(78)	(178)
Total, Fair Value	201	387
Total, Unrealized Losses	(83)	(180)
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	17	11
Less than 12 Months, Unrealized Losses	(2)
12 Months or Longer, Fair Value	22	85
12 Months or Longer, Unrealized Losses	(8)	(19)
Total, Fair Value	39	96
Total, Unrealized Losses	(10)	(19)
Asset-Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Total, Fair Value	639
Total, Unrealized Losses	(215)
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	13	3
Less than 12 Months, Unrealized Losses	(2)
12 Months or Longer, Fair Value	117	278
12 Months or Longer, Unrealized Losses	(116)	(180)
Total, Fair Value	130	281
Total, Unrealized Losses	(118)	(180)
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	53	61
Less than 12 Months, Unrealized Losses	(7)	(2)
12 Months or Longer, Fair Value	328	480
12 Months or Longer, Unrealized Losses	(75)	(110)
Total, Fair Value	381	541
Total, Unrealized Losses	(82)	(112)
Variable Interest Entities [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 Entities [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
12 Months or Longer, Fair Value	90
12 Months or Longer, Unrealized Losses	(26)
Total, Fair Value	93
Total, Unrealized Losses	(26)
Variable Interest Entities [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	62
Less than 12 Months, Unrealized Losses		(1)
12 Months or Longer, Fair Value	88	5
12 Months or Longer, Unrealized Losses	(15)
Total, Fair Value	97	67
Total, Unrealized Losses	(15)	(1)
Variable Interest Entities [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	7
Total, Fair Value	$ 31	$ 7