Income Taxes (Unrecognized Tax Benefit Rollforward) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Tax Disclosure [Abstract]
Additions based on current year tax positions	$ 1	$ 4
Additions based on prior year tax positions	1	4
Reductions for prior year tax positions	(1)	(1)
Reductions for settlements	(52)	(2)
Reductions for lapse of statute of limitations	(3)	(8)
Unrecognized tax benefit	$ 171	$ 225	$ 228