Leases - Additional Information Related to Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases	$ 323	$ 325
Operating cash flows from finance leases	25	24
Financing cash flows from finance leases	64	57
Right-of-use assets obtained in exchange for lease liabilities:
Operating leases	205	365
Finance leases	$ 45	$ 50
Weighted-average remaining lease term:
Operating leases	10 years 6 months	10 years 8 months 12 days
Finance leases	10 years 1 month 6 days	6 years 1 month 6 days
Weighted-average discount rate:
Operating leases	3.00%	3.00%
Finance leases	7.00%	8.00%