Commercial Paper Program (Details) (USD $)	1 Months Ended	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Line of Credit Facility [Line Items]
Size of total commercial paper program	$ 1,200,000,000	$ 1,200,000,000
Commitment fee		15 to 35 basis points, depending on credit rating and currently pay a commitment fee of 20 basis points
Commitment fee, minimum percentage to pay depending on credit rating		0.15%
Commitment fee, maximum percentage to pay depending on credit rating		0.35%
Special dividend (in usd per share)	$ 2.50	$ 1.02	$ 1.00	$ 0.94
Commercial Paper	457,000,000	457,000,000	0
Indebtedness to cash flow		4
3 Year Facility [Member]
Line of Credit Facility [Line Items]
Size of total commercial paper program	1,200,000,000	1,200,000,000
Commercial Paper [Member]
Line of Credit Facility [Line Items]
Commercial paper interest rate	0.48%	0.48%
Commercial Paper, Average Term		28 days
Funds available through debt instrument	$ 743,000,000	$ 743,000,000