Revenue Recognition - Reported Results Under ASC 606 (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Operating revenue	$ 5,570	$ 5,606	$ 5,578	$ 5,647	$ 5,778	$ 5,818	$ 5,902	$ 5,945	$ 22,401	$ 23,443	$ 17,656
Cost of services and products (exclusive of depreciation and amortization)									10,077	10,862	8,203
Selling, general and administrative									3,715	4,165	3,508
Interest expense									2,021	2,177	1,481
Income tax expense (benefit)									503	170	(849)
NET (LOSS) INCOME	$ 223	$ 302	$ 371	$ (6,165)	$ (2,412)	$ 272	$ 292	$ 115	$ (5,269)	$ (1,733)	$ 1,389
BASIC AND DILUTED LOSS PER COMMON SHARE
BASIC (in dollars per share)	$ 0.21	$ 0.28	$ 0.35	$ (5.77)	$ (2.26)	$ 0.25	$ 0.27	$ 0.11	$ (4.92)	$ (1.63)	$ 2.21
DILUTED (in dollars per share)	$ 0.21	$ 0.28	$ 0.35	$ (5.77)	$ (2.26)	$ 0.25	$ 0.27	$ 0.11	$ (4.92)	$ (1.63)	$ 2.21
WEIGHTED AVERAGE COMMON SHARES OUTSTANDING
BASIC (in shares)									1,071,441	1,065,866	627,808
DILUTED (in shares)									1,071,441	1,065,866	628,693
Impact of ASC 606 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Operating revenue										$ 39
Cost of services and products (exclusive of depreciation and amortization)										22
Selling, general and administrative										71
Interest expense										(9)
Income tax expense (benefit)										(12)
NET (LOSS) INCOME										$ (33)
BASIC AND DILUTED LOSS PER COMMON SHARE
BASIC (in dollars per share)										$ (0.03)
DILUTED (in dollars per share)										$ (0.03)
WEIGHTED AVERAGE COMMON SHARES OUTSTANDING
BASIC (in shares)										0
DILUTED (in shares)										0
ASC 605 Historical Adjusted Balances
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Operating revenue										$ 23,482
Cost of services and products (exclusive of depreciation and amortization)										10,884
Selling, general and administrative										4,236
Interest expense										2,168
Income tax expense (benefit)										158
NET (LOSS) INCOME										$ (1,766)
BASIC AND DILUTED LOSS PER COMMON SHARE
BASIC (in dollars per share)										$ (1.66)
DILUTED (in dollars per share)										$ (1.66)
WEIGHTED AVERAGE COMMON SHARES OUTSTANDING
BASIC (in shares)										1,065,866
DILUTED (in shares)										1,065,866