Occupancy Expense and Information Systems and Communications Expense - Summary of Future Minimum Lease Payments (Details) $ in Millions	Jun. 30, 2019 USD ($)
Operating Leases
2019 (excluding the first six months ended 2019)	$ 96
2020	186
2021	175
2022	151
2023	131
Thereafter	401
Total future minimum lease payments	1,140
Less imputed interest	(116)
Total	1,024
Finance Leases
2019 (excluding the first six months ended 2019)	21
2020	42
2021	42
2022	42
2023	30
Thereafter	0
Total future minimum lease payments	177
Less imputed interest	(25)
Total	152
2019 (excluding the first six months ended 2019)	117
2020	228
2021	217
2022	193
2023	161
Thereafter	401
Total future minimum lease payments	1,317
Less imputed interest	(141)
Total	$ 1,176