Leases - Operating ROU Assets and Liabilities (Details) $ in Millions	Mar. 31, 2019 USD ($)
Leases [Abstract]
Operating lease ROU assets	$ 767	[1]
Operating lease liabilities	$ 817
Weighted-average remaining lease term	7 years 6 months
Weighted-average discount rate (percent)	3.20%

[1] Reported net of level lease adjustments and exit cost obligations.