Occupancy Expense and Information Systems and Communications Expense - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2019
Lessee, Lease, Description [Line Items]
Lease liabilities	$ 1,156
Depreciation and amortization	842	$ 599	$ 526
Finance lease right-of-use asset	78	102
Finance lease liability	136	190
Accumulated amortization of finance lease right-of-use asset	56
Interest on lease liabilities	11	$ 17
Right-of-use assets	858
Lease liabilities	1,020
Operating leases not yet commenced	$ 484
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	10 years
Maximum
Lessee, Lease, Description [Line Items]
Operating leases not yet commenced, lease terms	15 years