CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Statement of Cash Flows [Abstract]
Net income (loss)	$ 466	$ (320)	$ 176
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Depreciation and amortization	802	870	850
Provision for doubtful accounts	0	1,434	1,449
Deferred income tax expense	150	200	41
Stock-based compensation expense	46	59	68
Impairment and restructuring charges, and acquisition-related costs	209	541	202
Litigation and investigation costs	38	23	293
Net gains on sales, consolidation and deconsolidation of facilities	(127)	(144)	(151)
Loss (gain) from early extinguishment of debt	(1)	164	0
Equity in earnings of unconsolidated affiliates, net of distributions received	(12)	(18)	(13)
Amortization of debt discount and debt issuance costs	45	44	41
Pre-tax loss (income) from discontinued operations	(4)	0	6
Other items, net	(21)	(18)	(1)
Changes in cash from operating assets and liabilities:
Accounts receivable	(134)	(1,448)	(1,604)
Inventories and other current assets	17	(35)	(83)
Income taxes	(3)	(38)	(8)
Accounts payable, accrued expenses and other current liabilities	(152)	(10)	(51)
Other long-term liabilities	(102)	26	40
Payments for restructuring charges, acquisition-related costs, and litigation costs and settlements	(163)	(125)	(691)
Net cash used in operating activities from discontinued operations, excluding income taxes	(5)	(5)	(6)
Net cash provided by operating activities	1,049	1,200	558
Cash flows from investing activities:
Purchases of property and equipment — continuing operations	(617)	(707)	(875)
Purchases of businesses or joint venture interests, net of cash acquired	(113)	(50)	(117)
Proceeds from sales of facilities and other assets	543	827	573
Proceeds from sales of marketable securities, long-term investments and other assets	199	36	62
Purchases of equity investments	(127)	(68)	(39)
Other long-term assets	15	(10)	(31)
Other items, net	(15)	(7)	(3)
Net cash provided by (used in) investing activities	(115)	21	(430)
Cash flows from financing activities:
Repayments of borrowings under credit facility	(950)	(970)	(1,895)
Proceeds from borrowings under credit facility	950	970	1,895
Repayments of other borrowings	(312)	(4,139)	(154)
Proceeds from other borrowings	23	3,795	760
Debt issuance costs	0	(62)	(12)
Distributions paid to noncontrolling interests	(288)	(258)	(218)
Proceeds from sale of noncontrolling interests	20	31	22
Purchases of noncontrolling interests	(647)	(729)	(186)
Proceeds from exercise of stock options and employee stock purchase plan	16	7	4
Other items, net	54	29	16
Net cash provided by (used in) financing activities	(1,134)	(1,326)	232
Net increase (decrease) in cash and cash equivalents	(200)	(105)	360
Cash and cash equivalents at beginning of period	611	716	356
Cash and cash equivalents at end of period	411	611	716
Supplemental disclosures:
Interest paid, net of capitalized interest	(976)	(939)	(932)
Income tax payments, net	$ (25)	$ (56)	$ (33)