Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012
Income Tax
Effective tax rate on income from continuing operations (as a percent)	29.60%	42.80%	27.10%	32.40%
Reductions for tax positions of prior years			$ 32
Valuation allowance	16		16		16
Gross unrecognized tax benefit (expense)	135		135		116
Unrecognized tax benefits (net of federal tax benefits) that would impact the effective tax rate	54		54		38
Increase (reduction) in interest and penalties	1	1	2	(4)
Accrued interest and penalties	38		38		36
Estimated decrease in amount of unrecognized tax benefits in next 12 months	98		98
State and Local
Income Taxes
State net operating losses	$ 38		$ 38