Debt (Details)	6 Months Ended				3 Months Ended
	Jun. 30, 2011 USD ($)	Jun. 30, 2011 CNY	Jun. 30, 2012 USD ($)	Dec. 31, 2011 USD ($)	Mar. 31, 2012 Notes 4.70% [Member] USD ($)	Mar. 31, 2012 Notes 4.75% [Member] USD ($)
Debt Instrument [Line Items]
Fair value of long-term debt			$ 3,600,000,000	$ 2,600,000,000
Par value of issued senior unsecured notes					250,000,000	500,000,000
Interest rate on debt					4.70%	4.75%
Proceeds from issuance of long-term debt and capital securities, net					247,000,000	495,000,000
Maturity date					Mar. 15, 2037	Mar. 15, 2042
Line of credit facility, maximum borrowing amount	$ 633,000,000	4,000,000,000
Line of credit facility number of installments	6	6
Line of credit facility final payment due, years from date of first advance	5	5