Regulation and Capital Adequacy - Consolidated Regulatory Capital Ratios (Parenthetical) (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2016	Dec. 31, 2015	Dec. 31, 2014
Regulation And Capital Adequacy [Abstract]
Goodwill	$ 3,669	$ 3,657
Identifiable intangible assets deducted from CET1 during transitional period	261	196
Identifiable Intangible Assets	$ 435	$ 491
Increased deductions due to transitional provisions, percentage	60.00%	40.00%	20.00%
Deferred tax liabilities associated with goodwill and identifiable intangible assets	$ 1,050	$ 1,040
Subordinated debt maturity period	5 years