Debt and Equity Transactions (Unaudited) (Details) (USD $)	1 Months Ended	3 Months Ended		9 Months Ended			1 Months Ended			4 Months Ended	9 Months Ended	1 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended
	Feb. 28, 2012	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Sep. 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]	Apr. 30, 2011 Senior Notes [Member] 8.25% Senior Notes Due 2015 [Member]	Sep. 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]	Sep. 30, 2012 Senior Notes [Member] 8.375% Senior Notes due 2017 [Member]	Sep. 30, 2011 Senior Notes [Member] Senior Notes Due 2031 [Member]	Sep. 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%	9.50%
Debt Instrument, Frequency of Periodic Payment							February 13 and August 13	March 1 and September 1	March 1 and September 1
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										104.125%		104.553%
Losses on early extinguishment of debt		0	0	168,000,000	68,000,000	7,000,000					55,000,000		168,000,000		6,000,000
Losses on early extinguishment of debt, net of tax						$ 6,000,000					$ 49,000,000		$ 149,000,000		$ 5,000,000
Losses on early extinguishment of debt effect on diluted earnings per share						$ 0.01					$ 0.05		$ 0.16		$ 0.01