Debt (Components of Notes Payable) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Short-term Debt [Line Items]
Principal amount	$ 59	$ 234	[1]
U.S. Commercial Paper [Member]
Short-term Debt [Line Items]
Principal amount	32	216
Effective interest rate	0.25%	0.24%
Bank Borrowings [Member]
Short-term Debt [Line Items]
Principal amount	$ 27	$ 18

[1] * Condensed from audited financial statements.