Leases (Lease Assets and Liabilities) (Details) - USD ($) $ in Millions		Dec. 31, 2019	Dec. 31, 2018
Operating leases		$ 1,812
Finance leases	[1]	468
Total leased assets		2,280
Current liabilities operating leases		362
Current liabilities finance leases		114
Noncurrent liabilities operating leases		1,471
Noncurrent liabilities finance leases		491
Total lease liabilities		2,438
Accumulated depreciation		20,330	$ 20,126
Finance Lease Assets [Member]
Accumulated depreciation		$ 797

[1] Finance lease assets are recorded net of accumulated amortization of $797 million as of December 31, 2019.