Leases (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Assets and Liabilities, Lessee [Abstract]
ROU asset	$ 1,521
Lease liability	1,673
Lease, Cost [Abstract]
Operating lease cost	72
Variable lease cost	8
Sublease income	(21)	$ (12)
Net lease cost	59
Cash paid for amounts included in the measurement of lease liability - operating cash flows	74
ROU assets obtained in exchange for new lease liabilities	$ 153
Weighted-average remaining lease term	8 years
Weighted-average discount rate	3.30%
Operating Lease Liabilities, Payments Due [Abstract]
Remainder of 2019	$ 209
2020	265
2021	240
2022	209
2023	196
Thereafter	825
Total undiscounted cash flows	1,944
Less: interest	271
Lease liability	$ 1,673