Leases - Lease Cost and Other Information (Details) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)
Lease, Cost [Abstract]
Operating lease cost	$ 33	$ 56
Short-term lease cost	1	1
Variable lease cost	2	3
Sublease income	(5)	(9)
Total lease cost	$ 31	51
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases		53
Right-of-use assets obtained in exchange for new operating lease liabilities		$ 214
Weighted-average remaining lease term
Finance leases	2 years 6 months	2 years 6 months
Operating leases	8 years 1 month 6 days	8 years 1 month 6 days
Weighted-average discount rate
Finance leases	6.50%	6.50%
Operating leases	5.73%	5.73%