Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2012 Y	Mar. 31, 2011	Dec. 31, 2011
Income Taxes
Effective tax rate on income from continuing operations (as a percent)	22.60%	23.70%
Maximum period for recognizing capital losses (in years)	5
Valuation allowance	$ 5		$ 5
Capital loss carryforwards	33
State net operating losses	39
Gross unrecognized tax benefit (expense)	84		184
Unrecognized tax benefits (net of federal tax benefits) that would impact the effective tax rate	15		38
Interest and penalties recognized	(5)		16
Accrued interest and penalties	32		37
Estimated decrease in amount of unrecognized tax benefits in next 12 months, low end of the range	50
Estimated decrease in amount of unrecognized tax benefits in next 12 months, high end of the range	$ 60