Debt (Narrative) (Details) (USD $)	1 Months Ended			6 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Feb. 28, 2011	Jun. 30, 2013	Jun. 30, 2013 4.10% Senior Notes Due 2022 [Member]	Dec. 31, 2012 4.10% Senior Notes Due 2022 [Member]	Mar. 31, 2012 4.10% Senior Notes Due 2022 [Member]	Jun. 30, 2013 Credit Facility [Member]	Feb. 28, 2011 Credit Facility [Member]
Debt Instrument [Line Items]
Senior Notes					$ 1,000,000,000	$ 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
Company exhanged Private Notes for Exchange Notes				999,500,000
Basis Points				35				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