Accumulated Other Comprehensive (Loss) Income (AOCI), Summary of AOCI Balances Including Amounts Reclassified from AOCI into Net Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Beginning Balance	$ 5,083
Other comprehensive (loss) income before reclassifications, net of tax	(85)	$ (6)	$ (193)
Amounts reclassified from AOCI, net of tax	51	41	41
Net current period other comprehensive (loss) income	(34)	35	(152)
Ending Balance	5,839	5,083
Accumulated Other Comprehensive Loss [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Beginning Balance	(691)	(726)	(574)
Ending Balance	(725)	(691)	(726)
Foreign Currency Translation Adjustments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Beginning Balance	(54)	(178)	(101)
Other comprehensive (loss) income before reclassifications, net of tax	(82)	124	(77)
Amounts reclassified from AOCI, net of tax	0	0	0
Net current period other comprehensive (loss) income	(82)	124	(77)
Ending Balance	(136)	(54)	(178)
Unrealized (Losses) Gains on Hedging Instruments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Beginning Balance	9	6	(8)
Other comprehensive (loss) income before reclassifications, net of tax	(17)	7	3
Amounts reclassified from AOCI, net of tax	(2)	(4)	11
Net current period other comprehensive (loss) income	(19)	3	14
Ending Balance	(10)	9	6
Unrecognized (Losses) Gains and Prior Service Cost, Net [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Beginning Balance	(646)	(554)	(465)
Other comprehensive (loss) income before reclassifications, net of tax	14	(137)	(119)
Amounts reclassified from AOCI, net of tax	53	45	30
Net current period other comprehensive (loss) income	67	(92)	(89)
Ending Balance	$ (579)	$ (646)	$ (554)