Leases - Cash Flow From Lease Transactions (Details) - USD ($) $ in Millions		3 Months Ended
	Jan. 01, 2019	Mar. 31, 2019
Leases
(Gains) and losses on sale and leaseback transactions, net		$ (36)
Cash paid for amounts included in the measurement of lease liabilities
Operating cash outflows from finance leases		1
Financing cash outflows from finance leases		3
Operating cash outflows from operating leases		380
ROU assets obtained in exchange for new finance lease liabilities		153
ROU assets obtained in exchange for new operating lease liabilities	$ 156	$ 4,958
Weighted-average remaining lease term - finance leases		10 years 8 months 12 days
Weighted-average remaining lease term - operating leases		5 years 1 month 6 days
Weighted-average discount rate - finance leases		3.64%
Weighted-average discount rate - operating leases		3.34%