Income Taxes (Details 6) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Reconciliation of the Company's beginning and ending amount of unrecognized tax benefits
Balance at the beginning of the period	$ 118	$ 100
Additions based on tax positions related to the current year	21	8
Additions for tax positions of prior years	45	5
Reductions for tax positions of prior years	(1)	(16)
Settlements	(22)	(15)
Lapse of statute of limitations	(5)	(4)
Acquisitions		40
Balance at the end of the period	156	118
Unrecognized tax benefits that would impact effective tax rate	156
Uncertain Tax Positions
Accrued potential interest and penalties	6	6
Liability recorded for interest and penalties	$ 23	$ 19