Occupancy Expense and Information Systems and Communications Expense - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Jan. 01, 2019
Lessee, Lease, Description [Line Items]
Lease liabilities	$ 1,220
Depreciation and amortization	205
Finance lease right-of-use asset	94
Finance lease liability	160
Interest on lease liabilities	3
Accumulated amortization of finance lease right-of-use asset	40
Right-of-use assets	899
Lease liabilities	1,060
Operating leases not yet commenced	$ 497
Accounting Standards Update 2016-02
Lessee, Lease, Description [Line Items]
Right-of-use assets		$ 910
Lease liabilities		$ 1,060
Minimum
Lessee, Lease, Description [Line Items]
Operating leases not yet commenced, lease terms	11 years
Maximum
Lessee, Lease, Description [Line Items]
Operating leases not yet commenced, lease terms	15 years