Leases - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Jan. 01, 2019
Lessee, Lease, Description [Line Items]
Operating lease, right-of-use assets	$ 422
Operating lease, liability	530
Operating cash flows paid for amounts included in the measurement of lease liabilities	57
Lease assets obtained in exchange for lease liabilities	$ 22
Operating lease, weighted-average remaining lease term	4 years
Operating lease, weighted-average discount rate	4.00%
Accounting Standards Update 2016-02
Lessee, Lease, Description [Line Items]
Operating lease, right-of-use assets		$ 458
Operating lease, liability		$ 574