Leases - Lease Costs (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Leases [Abstract]
Operating lease expense	$ 131
Amortization of right-of-use assets	1
Short-term lease expense	13
Variable lease expense	26
Sublease income	(1)
Total lease expense	$ 170
Weighted average remaining lease term, Operating leases	4 years 9 months 25 days
Weighted average remaining lease term, Finance leases	3 years 2 months 4 days
Weighted average discount rate, Operating leases	4.24%
Weighted average discount rate, Finance leases	4.02%