Occupancy Expense and Information Systems and Communications Expense - Summary of Lease Cost (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Finance lease:
Amortization of right-of-use assets	$ 21
Interest on lease liabilities	11	$ 17
Total finance lease expense	32
Sublease income	(9)
Net finance lease expense	23
Operating lease:
Operating lease expense	179
Sublease income	(6)
Net operating lease expense	173
Net lease expense	196
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from finance leases	11
Operating cash flows from operating leases	201
Financing cash flows from finance leases	54
Right-of-use assets obtained in exchange for new lease obligations:
Operating leases	120
Finance leases	$ 0