Leases (Commitments Relating to Noncancellable Lease Obligations) (Details) - USD ($) $ in Millions		Sep. 30, 2019	Dec. 31, 2018
Operating Leases
2019 (remaining three months)		$ 63
2020		177
2021		133
2022		110
2023		87
Thereafter		274
Total minimum future payments		844
Less: Imputed interest		(210)
Total liabilities		634
Less: current portion		(137)
Long-term liabilities		497
Finance Leases
2019 (remaining three months)		3
2020		13
2021		11
2022		10
2023		17
Thereafter		164
Total minimum future payments		218
Less: Imputed interest		(96)
Total liabilities		122
Less: Current portion		(7)
Long-term liabilities		115
Financing Obligations
2019 (remaining three months)		4
2020		11
2021		12
2022		12
2023		12
Thereafter		236
Total minimum future payments		287
Less: Imputed interest		(130)
Total financing obligations		157
Less: Current portion		(2)
Long-term liabilities		$ 155
Lease Accounting Prior to Adoption of ASC 842 [Member]
Operating Leases
2019	[1]		$ 188
2020	[1]		157
2021	[1]		121
2022	[1]		98
2023	[1]		79
Thereafter	[1]		234
Total minimum future payments	[1]		877
Capital Leases
2019			12
2020			10
2021			8
2022			7
2023			14
Thereafter			121
Total minimum future payments			172
Less: Imputed interest			(80)
Total capital lease obligations			92
Less: Current portion			(8)
Long-term capital lease obligations			84
Financing Obligations
2019			12
2020			9
2021			10
2022			10
2023			10
Thereafter			106
Total minimum future payments			157
Less: Imputed interest			(18)
Total financing obligations			139
Less: Current portion			(5)
Long-term liabilities			$ 134

[1] Minimum lease payments have not been reduced by minimum sublease rentals due in the future, which are considered immaterial.