Financial Guarantees (Textual) (Details) (Financial Standby Letter of Credit [Member], USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Financial Standby Letter of Credit [Member]
Financial Guarantees (Textual) [Abstract]
Letters of credit outstanding	$ 47	$ 43	$ 46
Expiry of letters of credit, maximum	5 years

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

No definition available.

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant