Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended			9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Jun. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Income Taxes
Effective tax rate on income from continuing operations (as a percent)	25.50%	23.80%		26.40%	30.30%
Reductions for tax positions of prior years			$ (32)	$ 32
Valuation allowance	16			16		16
Gross unrecognized tax benefit (expense)	181			181		116
Unrecognized tax benefits (net of federal tax benefits) that would impact the effective tax rate	55			55		38
Estimated decrease in amount of unrecognized tax benefits in next 12 months	143			143
Increase (reduction) in interest and penalties	2	0		4	(4)
Accrued interest and penalties	40			40		36
State and Local
Income Taxes
State net operating losses	$ 38			$ 38