Risk Management Interest Rate Risk Managment (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended			1 Months Ended		9 Months Ended		9 Months Ended
	Jun. 30, 2012	Sep. 30, 2012	Dec. 31, 2011	Mar. 31, 2012 Swap Agreements (i) [Member] agreements	Sep. 30, 2012 Swap Agreements (i) [Member]	Sep. 30, 2012 Swap Agreements (ii) [Member] agreements	Aug. 13, 2012 Interest rate swap on 3.45% senior notes due February 15, 2023 [Member]	Sep. 30, 2012 Interest rate swap on 5.85% senior notes due September 15, 2012 [Member]	Sep. 30, 2012 Senior notes due September 1, 2022 [Member]	Mar. 14, 2012 Senior Notes [Member] 7.125% senior notes due March 15, 2012 [Member]		Dec. 31, 2011 Senior Notes [Member] 7.125% senior notes due March 15, 2012 [Member]
Derivative [Line Items]
Notional amount of interest rate fair value hedge derivatives		$ 5,525	$ 5,325		$ 500	$ 200	$ 100
Interest rate, stated percentage									3.95%	7.125%	[1]	7.125%
Number of fixed to variable interest rate swap agreements				4		2
Notional principal of terminated swaps	100							100
Proceeds from early termination of swaps	$ 53

[1] On March 14, 2012, we completed a public offering of $1.0 billion in principal amount of 3.95% senior notes due September 1, 2022. We received proceeds from the issuance of the notes, after deducting the underwriting discount, of $994 million, and we used the proceeds both to repay our $450 million 7.125% senior notes that matured on March 15, 2012 and to reduce the borrowings under our commercial paper program.