Leases (Summary of Leases) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Jan. 01, 2019
Finance Leases
2020	$ 26
2021	25
2022	23
2023	23
2024	23
Remaining years	243
Future minimum lease payments	363
Amount representing interest or discounts	(86)
Total lease liabilities	277
Operating Leases
2020	488
2021	260
2022	167
2023	111
2024	84
Remaining years	299
Future minimum lease payments	1,409
Amount representing interest or discounts	(148)
Total lease liabilities	$ 1,261	$ 1,415