Leases - Narrative (Details) - USD ($) $ in Millions	Mar. 31, 2019	Jan. 01, 2019
Lessee, Lease, Description [Line Items]
Operating lease liabilities	$ 8,562
Operating lease ROU assets	$ 8,272
Operating lease, general lease terms (or less)	20 years
Additional operating leases not yet commenced	$ 1,300
Operating leases not yet commenced, lease terms (up to)	25 years
Accounting Standards Update 2016-02
Lessee, Lease, Description [Line Items]
Operating lease liabilities		$ 8,200
Operating lease ROU assets		$ 8,100