Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 103	$ 95
Other intangible assets, accumulated amortization	100	97
Service Concession Asset, Accumulated Depreciation	$ 52	$ 34
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	1,200,000,000	1,200,000,000
Common stock, shares issued (in shares)	815,894,592	815,846,621
Common stock, shares outstanding (in shares)	658,997,660	666,808,790
Treasury stock, shares (in shares)	156,896,932	149,037,831
Variable Interest Entity [Line Items]
Non-recourse debt - current balance at variable interest entities	$ 2,220	$ 2,505
Consolidated Variable Interest Entities [Member]
Variable Interest Entity [Line Items]
Non-recourse debt - current balance at variable interest entities	247	261
Non-recourse debt - noncurrent, balance at variable interest entities	$ 1,503	$ 1,539