CONSOLIDATED BALANCE SHEETS (Unaudited) (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 47	$ 74
Property and equipment, accumulated depreciation	1,578	1,416
Customer relationships, accumulated amortization	5,862	5,660
Other intangibles, accumulated amortization	$ 2,530	$ 2,365
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, authorized shares (in shares)	100,000,000	100,000,000
Preferred stock, issued shares (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Class A
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, authorized shares (in shares)	1,600,000,000	1,600,000,000
Common stock, issued shares (in shares)	389,000,000	372,000,000
Common stock, outstanding shares (in shares)	379,000,000	367,000,000
Treasury stock, shares	10,000,000	5,000,000
Class B
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, authorized shares (in shares)	625,000,000	625,000,000
Common stock, issued shares (in shares)	543,000,000	544,000,000
Common stock, outstanding shares (in shares)	543,000,000	544,000,000