Accumulated Other Comprehensive Loss (Details 2) - USD ($) $ 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
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest expense									$ 2,021	$ 2,177	$ 1,481
Other income, net									(19)	44	12
(LOSS) INCOME BEFORE INCOME TAX EXPENSE									(4,766)	(1,563)	540
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
Reclassification out of Accumulated Other Comprehensive Income | Interest rate swap
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest expense									2
Reclassification out of Accumulated Other Comprehensive Income | Net actuarial loss
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income, net									224	178
Reclassification out of Accumulated Other Comprehensive Income | Prior service cost
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income, net									8	12
Reclassification out of Accumulated Other Comprehensive Income | Defined Benefit Plans
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
(LOSS) INCOME BEFORE INCOME TAX EXPENSE									234	190
Income tax expense (benefit)									(57)	(47)
NET (LOSS) INCOME									$ 177	$ 143