Leases - Lease Costs (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Jan. 01, 2019
Lease, Cost [Abstract]
ROU asset	$ 247	$ 156
Operating lease costs	21
Short-term lease costs	81
Variable lease costs	60
Total lease costs	162
ROU assets obtained in exchange for new operating lease liabilities(d)	$ 268