CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities:
Net income	$ 824	$ 696	$ 753
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	270	249	304
Provision for doubtful accounts	315	308	297
Deferred income tax provision	9	37	112
Stock-based compensation expense	79	69	52
Gain on disposition of business	0	(118)	(334)
Other, net	(6)	(6)	6
Changes in operating assets and liabilities:
Accounts receivable	(298)	(343)	(262)
Accounts payable and accrued expenses	(8)	56	(24)
Income taxes payable	16	42	(41)
Termination of interest rate swap agreements	0	54	0
Other assets and liabilities, net	(26)	25	(42)
Net cash provided by operating activities	1,175	1,069	821
Cash flows from investing activities:
Business acquisitions, net of cash acquired	(581)	(139)	(67)
Proceeds from disposition of business	1	270	0
Escrow proceeds associated with disposition of business	25	0	0
Capital expenditures	(252)	(293)	(263)
Investment in equity method investee	0	0	(33)
Decrease in investments and other assets	2	10	1
Net cash used in investing activities	(805)	(152)	(362)
Cash flows from financing activities:
Proceeds from borrowings	205	1,869	2,453
Repayments of debt	(182)	(1,724)	(2,537)
Purchases of treasury stock	(465)	(590)	(224)
Exercise of stock options	130	73	60
Employee payroll tax withholdings on stock issued under stock-based compensation plans	(23)	(10)	(7)
Dividends paid	(247)	(223)	(212)
Distributions to noncontrolling interests	(51)	(41)	(42)
Sale of noncontrolling interest in subsidiary	4	0	63
Payment of deferred business acquisition consideration	(3)	0	(51)
Other financing activities, net	40	(45)	(21)
Net cash used in financing activities	(592)	(691)	(518)
Net change in cash and cash equivalents	(222)	226	(59)
Cash and cash equivalents, beginning of year	359	133	192
Cash and cash equivalents, end of year	$ 137	$ 359	$ 133