Debt and Equity Transactions (Unaudited) (Details) (USD $)	1 Months Ended	3 Months Ended		6 Months Ended								3 Months Ended	4 Months Ended	1 Months Ended	6 Months Ended	3 Months Ended
	Feb. 28, 2012	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2011 Long-term Debt [Member] 8.25% Senior Notes Due 2015 [Member]	Jun. 30, 2011 Long-term Debt [Member] Senior Notes Due 2031 [Member]	Jun. 30, 2011 Line of Credit [Member]	Feb. 28, 2012 Senior Notes [Member] 1.40% Senior Notes due 2015 [Member]	Feb. 28, 2012 Senior Notes [Member] 2.15% Senior Notes due 2017 [Member]	Feb. 28, 2012 Senior Notes [Member] 3.55% Senior Notes due 2022 [Member]	Jun. 30, 2011 Senior Notes [Member] 8.25% Senior Notes Due 2015 [Member]	Apr. 30, 2011 Senior Notes [Member] 8.25% Senior Notes Due 2015 [Member]	Mar. 31, 2012 Senior Notes [Member] 8.375% Senior Notes due 2017 [Member]	Jun. 30, 2012 Senior Notes [Member] 8.375% Senior Notes due 2017 [Member]	Jun. 30, 2011 Senior Notes [Member] Senior Notes Due 2031 [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%	9.50%
Debt Instrument, Redemption Date													Apr. 01, 2011	Mar. 14, 2012
Extinguishment of Debt, Amount													1,100,000,000	3,000,000,000		35,000,000
Early Repayment of Senior Debt																49,000,000
Redemption price percentage to principal amount (in hundredths)													104.125%	104.553%
Losses on early extinguishment of debt		0	61,000,000	168,000,000	68,000,000	55,000,000	6,000,000	7,000,000				55,000,000			168,000,000	6,000,000
Loss on early extinguishment of debt, effect on net income attributable to common stockholders						$ 49,000,000	$ 5,000,000	$ 6,000,000				$ 49,000,000			$ 149,000,000	$ 5,000,000
Loss on early extinguishment of debt, effect on net income per diluted share (in dollars per share)						$ 0.05	$ 0.01	$ 0.01				$ 0.05			$ 0.16	$ 0.01