Leases - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Dec. 31, 2018
Leases [Abstract]
Leases and rental expense under operating lease right of use assets	$ 94
Total lease and rental expenses related to finance lease right of use assets	6
Operating lease expense	84
Operating cash flows from operating leases	$ 85
Operating lease commitments		$ 1,300
Finance lease commitments		$ 104