Consolidated Statement of Cash Flows - USD ($) $ in Millions	3 Months Ended				6 Months Ended		9 Months Ended		12 Months Ended
	Mar. 31, 2019		Mar. 31, 2018		Jun. 30, 2019	Jun. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Cash flows from operating activities:
Net income (loss)	$ 193		$ 100		$ 409	$ 270	$ 652	$ 421	$ 860		$ 622		$ 366
Adjustments to reconcile net income (loss) to net cash provided by (used for) operating activities:
Depreciation, amortization and accretion	394		374		787	753	1,175	1,138	1,572		1,527		1,241
(Gains) losses on retirement of long-term obligations	1	[1]	71	[1]	2	74	2	106	2	[2]	106	[2]	4	[3]
Amortization of deferred financing costs and other non-cash interest	1		2		1	4	1	5	1		7		9
Stock-based compensation expense	29		23		62	47	91	79	117		103		92
Asset write-down charges	6		3		12	9	13	18	19		26		17
Deferred income tax (benefit) provision	1		1		1	1	2	2	2		2		15
Other non-cash adjustments, net	2		2		3	1	4	2	(2)		2		(2)
Changes in assets and liabilities, excluding the effects of acquisitions:
Increase (decrease) in accrued interest	(41)		(28)		18	22	(38)	(31)	21		16		35
Increase (decrease) in accounts payable	(5)		(5)		6	3	37	31	19		37		(34)
Increase (decrease) in other liabilities	(7)		(43)		77	76	179	179	254		271		234
Decrease (increase) in receivables	(43)		(5)		(89)	(59)	(166)	(74)	(96)		(105)		71
Decrease (increase) in other assets	(19)		(43)		(62)	(91)	(62)	(103)	(71)		(114)		(16)
Net cash provided by (used for) operating activities	512		452		1,227	1,110	1,890	1,773	2,698		2,500		2,032
Cash flows from investing activities:
Capital expenditures	(480)		(370)		(998)	(762)	(1,537)	(1,239)	(2,057)		(1,739)		(1,217)
Payments for acquisitions, net of cash acquired	(10)		(14)		(13)	(18)	(15)	(26)	(17)		(42)		(9,260)
Other investing activities, net	1		0		1	3	3	(14)	(7)		(12)		(5)
Net cash provided by (used for) investing activities	(489)		(384)		(1,010)	(777)	(1,549)	(1,279)	(2,081)		(1,793)		(10,482)
Cash flows from financing activities:
Proceeds from issuance of long-term debt	996		1,743		995	1,743	1,895	2,743	1,894		2,742		3,093
Principal payments on debt and other long-term obligations	(25)		(32)		(36)	(47)	(59)	(76)	(86)		(105)		(119)
Purchases and redemptions of long-term debt	(12)		(1,318)		(12)	(1,318)	(12)	(2,346)	(12)		(2,346)		0
Borrowings under revolving credit facility	710		170		1,195	485	1,585	1,290	2,110		1,820		2,820
Payments under revolving credit facility	(1,140)		(1,050)		(1,785)	(1,150)	(2,270)	(1,465)	(2,660)		(1,725)		(1,840)
Proceeds from Issuance of Commercial Paper	0				500		0		155		0
Payments for financing costs	(10)		(15)		(14)	(20)	(24)	(33)	(24)		(31)		(29)
Net proceeds from issuance of common stock			843			841		841	0		841		4,221
Net proceeds from issuance of preferred stock									0		0		1,608
Purchases of common stock	(42)		(33)		(43)	(34)	(44)	(34)	(44)		(34)		(23)
Dividends/distributions paid on common stock	(477)		(443)		(944)	(879)	(1,415)	(1,315)	(1,912)		(1,782)		(1,509)
Dividends paid on preferred stock	(28)		(28)		(57)	(57)	(85)	(85)	(113)		(113)		(30)
Net cash provided by (used for) financing activities	(28)		(163)		(201)	(436)	(429)	(480)	(692)		(733)		8,192
Net increase (decrease) in cash, cash equivalents, and restricted cash from continuing operations	(5)		(95)		16	(103)	(88)	14	(75)		(26)		(258)
Effect of exchange rate changes on cash	0		0		0	(1)	0	(1)	0		(1)		1
Cash, Cash Equivalents and Restricted Cash - Beginning of Period	413		440		413	440	413	440	413		440		697
Cash, Cash Equivalents and Restricted Cash - End of Period	$ 408		$ 345		$ 429	$ 336	$ 325	$ 453	$ 338		$ 413		$ 440

[1] The sum of quarterly information may not agree to year-to-date information due to rounding.

[2] Inclusive of the write-off of the respective deferred financing costs.

[3] The losses represent write-off of deferred financing costs.