Revenue Recognition - Reported Results Under ASC 606 (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
OPERATING REVENUES	$ 5,818	$ 4,034	$ 17,665	$ 12,333
Cost of services and products (exclusive of depreciation and amortization)	2,672	1,927	8,205	5,705
Selling, general and administrative	967	710	3,191	2,404
Interest expense	557	362	1,638	1,000
Income tax expense	57	47	123	214
Net income	$ 272	$ 92	$ 679	$ 272
BASIC AND DILUTED EARNINGS PER COMMON SHARE
BASIC (in dollars per share)	$ 0.25	$ 0.17	$ 0.64	$ 0.50
DILUTED (in dollars per share)	$ 0.25	$ 0.17	$ 0.63	$ 0.50
WEIGHTED-AVERAGE COMMON SHARES OUTSTANDING
BASIC (in shares)	1,066,904	541,521	1,065,410	541,113
DILUTED (in shares)	1,072,351	541,963	1,069,726	541,879
Other current assets	$ 1,237		$ 1,237		$ 941
Other long-term assets, net	1,014		1,014
Deferred revenue	2,547		2,547
Deferred income taxes, net	2,502		2,502		2,413
Other long-term liabilities	1,075		1,075
Retained earnings	777		777		$ 1,103
Impact of ASC 606 | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
OPERATING REVENUES	(14)		12
Cost of services and products (exclusive of depreciation and amortization)	8		18
Selling, general and administrative	16		42
Interest expense	(7)		(7)
Income tax expense	(8)		(11)
Net income	$ (23)		$ (30)
BASIC AND DILUTED EARNINGS PER COMMON SHARE
BASIC (in dollars per share)	$ (0.02)		$ (0.03)
DILUTED (in dollars per share)	$ (0.02)		$ (0.03)
WEIGHTED-AVERAGE COMMON SHARES OUTSTANDING
BASIC (in shares)	0		0
DILUTED (in shares)	0		0
Other current assets	$ (390)		$ (390)
Other long-term assets, net	(93)		(93)
Deferred revenue	(101)		(101)
Deferred income taxes, net	(127)		(127)
Other long-term liabilities	122		122
Retained earnings	(377)		(377)
ASC 605 Historical Adjusted Balances
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
OPERATING REVENUES	5,804		17,677
Cost of services and products (exclusive of depreciation and amortization)	2,680		8,223
Selling, general and administrative	983		3,233
Interest expense	550		1,631
Income tax expense	49		112
Net income	$ 249		$ 649
BASIC AND DILUTED EARNINGS PER COMMON SHARE
BASIC (in dollars per share)	$ 0.23		$ 0.61
DILUTED (in dollars per share)	$ 0.23		$ 0.60
WEIGHTED-AVERAGE COMMON SHARES OUTSTANDING
BASIC (in shares)	1,066,904		1,065,410
DILUTED (in shares)	1,072,351		1,069,726
Other current assets	$ 847		$ 847
Other long-term assets, net	921		921
Deferred revenue	2,446		2,446
Deferred income taxes, net	2,375		2,375
Other long-term liabilities	1,197		1,197
Retained earnings	$ 400		$ 400