Debt (Narrative) (Details) (USD $)	1 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Feb. 28, 2011	Sep. 30, 2012	Sep. 30, 2012 4.10% Senior Notes Due 2022 [Member]	Mar. 31, 2012 4.10% Senior Notes Due 2022 [Member]	Oct. 30, 2012 Credit Facility [Member]	Sep. 30, 2012 Credit Facility [Member]	Feb. 28, 2011 Credit Facility [Member]
Debt Instrument [Line Items]
Senior Notes					$ 1,000,000,000	$ 1,000,000,000
Debt instrument, interest rate, stated percentage					4.10%	4.10%
Senior notes redemption date	Dec. 15, 2021		Feb. 01, 2016
Principal amount of notes to be redeemed then outstanding	100.00%
Duration of assumed year, days	360 days
Duration of assumed month, days		30 days
Basis Points				35			200	200
Purchase price upon exercise of option	101.00%
Unsecured revolving credit facility, borrowing capacity			$ 1,500,000,000						$ 2,000,000,000
Debt percentage of capital structure			60.00%
EBITDA to Interest Expense Ratio			3.5