Occupancy Expense and Information Systems and Communications Expense - Narrative (Details) ft² in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($) ft²	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Occupancy Expense and Information Systems and Communications Expense [Abstract]
Depreciation	$ 443	$ 417	$ 401
Property Subject to or Available for Operating Lease [Line Items]
Capital lease obligation	231	624
Interest expense on capital lease	32	38	40
Accumulated amortization on capital lease	334	426
Sublease rental expense	190	204	224
Sublease revenue	4	$ 6	$ 6
Future minimum sublease rental revenue on capital lease	48
Future minimum sublease rental revenue on operating lease	$ 20
One Lincoln Street
Property Subject to or Available for Operating Lease [Line Items]
Leased area (in sqft) | ft²	1,025
Noncancelable capital leases expiration	20 years
Sublease building (in sqft) | ft²	127