Debt and Equity Transactions (Unaudited) (Details) (USD $)	1 Months Ended	3 Months Ended								4 Months Ended	1 Months Ended
	Feb. 28, 2012	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2011 Line of Credit [Member]	Mar. 31, 2012 Long-term Debt [Member]	Jun. 30, 2011 Long-term Debt [Member]	Feb. 28, 2012 Long-term Debt [Member] 1.40% Senior Notes due 2015 [Member]	Feb. 28, 2012 Long-term Debt [Member] 2.15% Senior Notes due 2017 [Member]	Feb. 28, 2012 Long-term Debt [Member] 3.55% Senior Notes due 2022 [Member]	Apr. 30, 2011 Long-term Debt [Member] 8.25% Senior Notes Due 2015 [Member]	Mar. 31, 2012 Long-term Debt [Member] 8.375% Senior Notes due 2017 [Member]
Extinguishment of Debt [Line Items]
Face amount of senior notes sold							$ 500,000,000	$ 500,000,000	$ 2,000,000,000
Proceeds from Issuance of Long-term Debt	2,970,000,000
Debt Instrument, Interest Rate (percent)							1.40%	2.15%	3.55%	8.25%	8.375%
Debt Instrument, Redemption Date										Apr. 01, 2011	Mar. 14, 2012
Extinguishment of Debt, Amount										1,100,000,000	3,000,000,000
Transfer of Funds to Restricted Cash										1,200,000,000
Redemption price percentage to principal amount (in hundredths)										104.125%	104.553%
Losses on early extinguishment of debt		168,000,000	7,000,000	7,000,000	168,000,000	55,000,000
Loss on early extinguishment of debt, effect on net income attributable to common stockholders				$ 6,000,000	$ 149,000,000	$ 49,000,000
Loss on early extinguishment of debt, effect on net income per diluted share (in dollars per share)				$ 0.01	$ 0.16	$ 0.05