Revolving Credit Facilities Schedule of Short term debt (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Short-term Debt [Line Items]
Average daily amount of short-term debt outstanding	$ 9	$ 4	$ 2
Weighted daily average interest rate	0.40%	0.40%	0.40%
Maximum amount outstanding during the year	$ 54	$ 44	$ 44