Leases - Supplemental Cash Flow and Other Information Related to Leases (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Leases [Abstract]
Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases	$ 149	$ 141
Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from finance leases	5	6
Cash paid for amounts included in the measurement of lease liabilities: Financing cash flows from finance leases	4	5
Right-of-use assets obtained in exchange for new finance lease liabilities	46	22
Right-of-use assets obtained in exchange for new operating lease liabilities	$ 118	$ 119