Financing (Details) (USD $)	12 Months Ended			1 Months Ended		1 Months Ended		1 Months Ended
	Dec. 31, 2011 day	Dec. 31, 2010	Dec. 31, 2009	Mar. 31, 2011 Fixed Rate Note Due 2016 [Member]	Dec. 31, 2011 Fixed Rate Note Due 2016 [Member]	Mar. 31, 2011 Fixed Rate Note Due 2021 [Member]	Dec. 31, 2011 Fixed Rate Note Due 2021 [Member]	Mar. 31, 2011 Fixed Rate Note Due 2041 [Member]	Dec. 31, 2011 Fixed Rate Note Due 2041 [Member]
Long-Term Debt [Line Items]
Long-term Debt, Gross	$ 1,000,000,000				$ 300,000,000		$ 300,000,000		$ 400,000,000
Unaccreted Discount	(1,000,000)
Long-term debt	999,034,000	0
Debt Instrument, Interest Rate, Effective Percentage					3.12%		4.63%		6.01%
Debt Instrument, Face Amount				300,000,000		300,000,000		400,000,000
Debt Instrument, Interest Rate, Stated Percentage				3.10%		4.60%		5.95%
Debt Instrument, Maturity Date				Mar. 15, 2016		Mar. 15, 2021		Mar. 15, 2041
Change of Control Repurchase Price Percentage of Principal	101.00%
Debt Instrument, Fair Value	1,069,800,000	0
Other Financing Arrangements [Abstract]
Number of days due from receivable	30
Sale of receivables	738,200,000	637,500,000	449,800,000
Proceeds from sale and collection of receivables	686,500,000	595,700,000	426,300,000
Receivables from sale of receivables	162,900,000	127,400,000
Cash received from financing provider that has not been recognized as revenue	$ 33,300,000	$ 49,100,000