Integration and Restructuring Costs (Restructuring Activities) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Restructuring Reserve [Roll Forward]
Liability at beginning of period	$ 93	$ 92	$ 124
Expense Incurred	44	28	12
Cash Paid	(39)	(28)	(44)
Other	(5)	1
Liability at end of period	93	93	92
Severance
Restructuring Reserve [Roll Forward]
Liability at beginning of period	15	7
Expense Incurred	40	17
Cash Paid	(22)	(7)
Other	(1)	(2)
Liability at end of period	32	15	7
Future rent under non-cancelable leases and other costs
Restructuring Reserve [Roll Forward]
Liability at beginning of period	78	85
Expense Incurred	4	11
Cash Paid	(17)	(21)
Other	(4)	3
Liability at end of period	$ 61	$ 78	$ 85