Investments (Fair Value of Available-For-Sale Investments with Gross Unrealized Losses by Investment Type and Length of Time That Individual Securities Have Been in a Continuous Unrealized Loss Position) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Debt Securities [Member]
Less Than 12 Months, Fair Value	$ 1,581	$ 3,235
Less Than 12 Months, Gross Unrealized Losses	(23)	(65)
12 Months or Greater, Fair Value	49	32
12 Months or Greater, Gross Unrealized Losses	(1)	(2)
Total, Fair Value	1,630	3,267
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	(24)	(67)
State and Municipal Obligations [Member]
Less Than 12 Months, Fair Value	85	1,383
Less Than 12 Months, Gross Unrealized Losses	(1)	(40)
12 Months or Greater, Fair Value	21	18
12 Months or Greater, Gross Unrealized Losses	0	(2)
Total, Fair Value	106	1,401
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	(1)	(42)
Corporate Obligations [Member]
Less Than 12 Months, Fair Value	1,496	949
Less Than 12 Months, Gross Unrealized Losses	(22)	(11)
12 Months or Greater, Fair Value	28	14
12 Months or Greater, Gross Unrealized Losses	(1)	0
Total, Fair Value	1,524	963
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	(23)	(11)
U.S. Government and Agency Obligations [Member]
Less Than 12 Months, Fair Value		548
Less Than 12 Months, Gross Unrealized Losses		(8)
12 Months or Greater, Fair Value		0
12 Months or Greater, Gross Unrealized Losses		0
Total, Fair Value		548
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		(8)
U.S. Agency Mortgage-Backed Securities [Member]
Less Than 12 Months, Fair Value		355
Less Than 12 Months, Gross Unrealized Losses		(6)
12 Months or Greater, Fair Value		0
12 Months or Greater, Gross Unrealized Losses		0
Total, Fair Value		355
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses		(6)
Equity Securities [Member]
Less Than 12 Months, Fair Value	24	206
Less Than 12 Months, Gross Unrealized Losses	(7)	(14)
12 Months or Greater, Fair Value	3	11
12 Months or Greater, Gross Unrealized Losses	(1)	0
Total, Fair Value	27	217
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	$ (8)	$ (14)