Leases - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
Renewal term			7 years
Weighted-average remaining lease term (in years)			4 years 1 month 6 days
Weighted-average discount rate			3.30%
Total undiscounted future lease payment			$ 306
Total lease payments			$ 567
Future minimum payments receivable	$ 203
Operating lease rent expense	166	$ 159
Minimum [Member]
Lessee, Lease, Description [Line Items]
Leases not yet commenced lease term			5 years
Maximum [Member]
Lessee, Lease, Description [Line Items]
Leases not yet commenced lease term			15 years
Abandoned Leases [Member]
Lessee, Lease, Description [Line Items]
Total lease payments	$ 222		$ 178