Summary of Significant Accounting Policies - Goodwill (Details) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2015	Dec. 31, 2014
Accounting Policies [Abstract]
Goodwill impairment	$ 0
Accumulated impairment loss	0	$ 0
Goodwill [Roll Forward]
Goodwill, beginning balance		5,209,000,000	$ 5,216,000,000
Foreign currency adjustments		(9,000,000)	(7,000,000)
Goodwill, ending balance	5,200,000,000	5,200,000,000	5,209,000,000
Payments
Goodwill [Roll Forward]
Goodwill, beginning balance		3,440,000,000	3,444,000,000
Foreign currency adjustments		(3,000,000)	(4,000,000)
Goodwill, ending balance	3,437,000,000	3,437,000,000	3,440,000,000
Financial
Goodwill [Roll Forward]
Goodwill, beginning balance		1,769,000,000	1,772,000,000
Foreign currency adjustments		(6,000,000)	(3,000,000)
Goodwill, ending balance	$ 1,763,000,000	$ 1,763,000,000	$ 1,769,000,000