Goodwill and Other Intangible Assets - Gross Carrying Amount, Accumulated Amortization And Net Carrying Amount Of Other Intangible Assets (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015	Dec. 31, 2014
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 3,534	$ 3,300
Accumulated Amortization	(1,685)	(1,532)
Net Carrying Amount	1,849	1,768	$ 2,025
Client relationships
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	2,703	2,486
Accumulated Amortization	(1,312)	(1,198)
Net Carrying Amount	1,391	1,288
Core deposits
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	673	667
Accumulated Amortization	(273)	(246)
Net Carrying Amount	400	421
Other
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	158	147
Accumulated Amortization	(100)	(88)
Net Carrying Amount	$ 58	$ 59