CONSOLIDATED BALANCE SHEETS (Unaudited) (Parenthetical) - USD ($) shares in Millions, $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 42	$ 74
Property and equipment, accumulated depreciation	1,500	1,416
Customer relationships, accumulated amortization	5,765	5,660
Other intangibles, accumulated amortization	$ 2,445	$ 2,365
Class A common stock
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, authorized shares (in shares)	1,600	1,600
Common stock, issued shares (in shares)	374	368
Common stock, outstanding shares (in shares)	374	368
Class B common stock
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, authorized shares (in shares)	625	625
Common stock, issued shares (in shares)	544	544
Common stock, outstanding shares (in shares)	544	544