Debt (Narrative) (Details) (USD $)	0 Months Ended
	Dec. 16, 2013	Dec. 31, 2013 7.5% Senior Notes due 2018 [Member]	Dec. 31, 2012 7.5% Senior Notes due 2018 [Member]	Dec. 31, 2013 4.10% Senior Notes Due 2022 [Member]	Dec. 31, 2012 4.10% Senior Notes Due 2022 [Member]	Dec. 31, 2013 7.15% Senior Notes due 2018 [Member]	Dec. 31, 2012 7.15% Senior Notes due 2018 [Member]	Dec. 31, 2013 7.35% Senior Notes due 2017 [Member]	Dec. 31, 2012 7.35% Senior Notes due 2017 [Member]	Dec. 31, 2013 7.125% Senior Notes due 2017 [Member]	Dec. 31, 2012 7.125% Senior Notes due 2017 [Member]	Dec. 16, 2013 Credit Facility [Member]	Dec. 31, 2012 Credit Facility [Member]
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage		7.50%	7.50%	4.10%	4.10%	7.15%	7.15%	7.35%	7.35%	7.125%	7.125%
Senior notes redemption date	Dec. 01, 2018
Basis Points												1.50%	2.00%
Unsecured revolving credit facility, borrowing capacity	$ 2,000,000,000
Unsecured revolving credit facility, increase in current borrowing capacity potential												$ 500,000,000
Debt percentage of capital structure covenant	60.00%
Stated interest rate		7.50%	7.50%	4.10%	4.10%	7.15%	7.15%	7.35%	7.35%	7.125%	7.125%