Leases - Components of Operating Lease Costs (Details) $ in Millions	3 Months Ended
	Mar. 31, 2019 USD ($)
Leases [Abstract]
Operating lease cost	$ 32
Short-term lease cost	4
Variable lease cost	14
Sublease income	(14)
Total operating lease costs, net	36
Cash paid for amounts included in the measurement of operating lease liabilities	31
ROU assets recognized for new operating lease liabilities	$ 10