Leases (Other Information) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash paid for amounts included in the measurement of lease liabilities
Operating cash flows from operating leases	$ 52	$ 52
Operating cash flows from finance leases	1	3
Financing cash flows from finance leases	21	12
Leased assets obtained in exchange for new operating lease liabilities	41	48
Leased assets obtained in exchange for new finance lease liabilities	$ 16	$ 34