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	Sep. 30, 2013	Dec. 31, 2012
Debt Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 6,779	$ 1,240
Less Than 12 Months, Gross Unrealized Losses	(168)	(8)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	6,779	1,240
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	(168)	(8)
US Treasury and Government [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	676	183
Less Than 12 Months, Gross Unrealized Losses	(12)	(1)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	676	183
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	(12)	(1)
State and Municipal Obligations [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	2,114	362
Less Than 12 Months, Gross Unrealized Losses	(57)	(3)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	2,114	362
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	(57)	(3)
Corporate Obligations [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	2,730	695
Less Than 12 Months, Gross Unrealized Losses	(53)	(4)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	2,730	695
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	(53)	(4)
U.S. Agency Mortgage-Backed Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	927
Less Than 12 Months, Gross Unrealized Losses	(38)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	927
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	(38)
Non-U.S. Agency Mortgage-Backed Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	332
Less Than 12 Months, Gross Unrealized Losses	(8)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	332
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	(8)
Equity Securities [Member]
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	137	13
Less Than 12 Months, Gross Unrealized Losses	(13)	(1)
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	137	13
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses	$ (13)	$ (1)