Leases - Components of Lease Expense (Details) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)
Lease expense
Operating lease expense	$ 32	$ 66
Sublease income	(2)	(4)
Total lease expense cost	30	62
Cash paid for amounts included in the measurement of lease liabilities
Operating cash flows from operating leases	31	62
Right-of-use assets obtained in exchange for new operating lease liabilities	$ 63	$ 68
Weighted-average remaining lease term - operating leases	6 years 1 month 6 days	6 years 1 month 6 days
Weighted-average discount rate - operating leases	5.00%	5.00%