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, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Operating revenue	$ 5,778	$ 5,818	$ 5,902	$ 5,945	$ 5,323	$ 4,034	$ 4,090	$ 4,209	$ 23,443	$ 17,656	$ 17,470
Cost of services and products (exclusive of depreciation and amortization)									10,862	8,203	7,774
Selling, general and administrative									4,165	3,508	3,447
Interest expense									2,177	1,481	1,318
Attributable to income									170	(849)	394
Net (loss) income	$ (2,412)	$ 272	$ 292	$ 115	$ 1,117	$ 92	$ 17	$ 163	$ (1,733)	$ 1,389	$ 626
BASIC AND DILUTED LOSS PER COMMON SHARE
BASIC (in dollars per share)	$ (2.26)	$ 0.25	$ 0.27	$ 0.11	$ 1.26	$ 0.17	$ 0.03	$ 0.30	$ (1.63)	$ 2.21	$ 1.16
DILUTED (in dollars per share)	$ (2.26)	$ 0.25	$ 0.27	$ 0.11	$ 1.26	$ 0.17	$ 0.03	$ 0.30	$ (1.63)	$ 2.21	$ 1.16
WEIGHTED AVERAGE COMMON SHARES OUTSTANDING
BASIC (in shares)									1,065,866	627,808	539,549
DILUTED (in shares)									1,065,866	628,693	540,679
Other current assets	$ 918				$ 941				$ 918	$ 941
Other long-term assets, net	1,060								1,060
Deferred revenue	2,375								2,375
Deferred income taxes, net	2,395								2,395
Other long-term liabilities	1,099								1,099
Accumulated deficit	(1,643)				$ 1,103				(1,643)	$ 1,103
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)
Attributable to income									(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
Other current assets	(172)								$ (172)
Other long-term assets, net	(112)								(112)
Deferred revenue	71								71
Deferred income taxes, net	(131)								(131)
Other long-term liabilities	147								147
Accumulated deficit	(371)								(371)
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
Attributable to income									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
Other current assets	746								$ 746
Other long-term assets, net	948								948
Deferred revenue	2,446								2,446
Deferred income taxes, net	2,264								2,264
Other long-term liabilities	1,246								1,246
Accumulated deficit	$ (2,014)								$ (2,014)