Valuation and Qualifying Accounts (Details) (Allowance for doubtful accounts [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Allowance for doubtful accounts [Member]
Valuation and Qualifying Accounts
Balance at beginning of year	$ 50	$ 52	$ 27
Net charges to income	2	20	32
Deductions and other	(14)	(22)	(7)
Balance at end of year	$ 38	$ 50	$ 52