Occupancy Expense and Information Systems and Communications Expense - Summary of Future Minimum Lease Payments (Details) $ in Millions	Sep. 30, 2019 USD ($)
Operating Leases
2019 (excluding the first nine months ended 2019)	$ 48
2020	182
2021	175
2022	153
2023	133
Thereafter	393
Total future minimum lease payments	1,084
Less imputed interest	(107)
Total	977
Finance Leases
2019 (excluding the first nine months ended 2019)	10
2020	42
2021	42
2022	42
2023	30
Thereafter	0
Total future minimum lease payments	166
Less imputed interest	(22)
Total	144
2019 (excluding the first nine months ended 2019)	58
2020	224
2021	217
2022	195
2023	163
Thereafter	393
Total future minimum lease payments	1,250
Less imputed interest	(129)
Total	$ 1,121