Occupancy Expense and Information Systems and Communications Expense - Summary of Future Minimum Lease Payments Under Non-Cancelable Capital and Operating Leases (Details) $ in Millions	Dec. 31, 2016 USD ($)
Capital Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Capital leases due 2017	$ 57
Capital leases due 2018	53
Capital leases due 2019	46
Capital leases due 2020	45
Capital leases due 2021	45
Capital leases due thereafter	79
Capital leases due	325
Less amount representing interest payments	(76)
Present value of minimum lease payments	249
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
Operating leases due 2017	205
Operating leases due 2018	185
Operating leases due 2019	138
Operating leases due 2020	123
Operating leases due 2021	118
Operating leases due thereafter	380
Operating leases due	1,149
Total operating and capital leases due 2017	262
Total operating and capital leases due 2018	238
Total operating and capital leases due 2019	184
Total operating and capital leases due 2020	168
Total operating and capital leases due 2021	163
Total operating and capital leases due thereafter	459
Total operating and capital leases due	$ 1,474