Debt (Narrative) (Details) (USD $)	3 Months Ended
	Mar. 31, 2012
Line of credit facility, maximum borrowing capacity	$ 2,000,000,000
Covenant terms, terms favorably reduced, period	2 years
Line of credit facility, current borrowing capacity	1,000,000,000
Loans payable	1,000,000,000
6.75% Senior Notes Due 2013 [Member]
Debt Instrument, Face Amount	$ 450,000,000
Stated interest rate	6.75%
Maximum [Member] | 6.75% Senior Notes Due 2013 [Member]
Tender offer, offering price per unit of principal	1.0025
Minimum [Member] | 6.75% Senior Notes Due 2013 [Member]
Tender offer, offering price per unit of principal	0.9725