Occupancy Expense and Information Systems and Communications Expense - Summary of Future Minimum Lease Payments (Details) $ in Millions	Mar. 31, 2019 USD ($)
Operating Leases
2019 (excluding the first quarter of 2019)	$ 144
2020	185
2021	174
2022	151
2023	131
Thereafter	400
Total future minimum lease payments	1,185
Less imputed interest	(125)
Total	1,060
Finance Leases
2019 (excluding the first quarter of 2019)	31
2020	42
2021	42
2022	42
2023	30
Thereafter	0
Total future minimum lease payments	187
Less imputed interest	(27)
Total	160
2019 (excluding the first quarter of 2019)	175
2020	227
2021	216
2022	193
2023	161
Thereafter	400
Total future minimum lease payments	1,372
Less imputed interest	(152)
Total	$ 1,220