Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016 USD ($) Segment state ATM Branch CallCentre $ / shares	Dec. 31, 2015 USD ($) $ / shares	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Accounting Policies [Line Items]
Common shares, par value (in dollars per share) | $ / shares	$ 1	$ 1
Consolidated total assets of the Company	$ 136,453,000,000	$ 95,131,000,000
Number of retail branches | Branch	1,217
Number of automated teller machines | ATM	1,593
Number of states with automated teller machines | state	15
Number of telephone banking call center services group | CallCentre	1
Number of business groups | Segment	2
Number of days to designate the loan as nonaccrual for commercial loan payment due period	90 days
Number of days to designate commercial loans will be charged off in full or charged down to the fair value of the underlying collateral payment due period	180 days
Number of days to designate the loan as nonaccrual for consumer payment due period	120 days
Second lien home equity loan with associated first lien due period	120 days
Number of days to designate the charge-off policy for most consumer loans taking effect, payment due period	120 days
Number of days to designate home equity and residential mortgage loans to get charged down to the fair value of the underlying collateral payment due period	180 days
Number of days to designate charge-off policy for credit card loans and similar unsecured products taking effect, payment due period	180 days
Threshold period by which amortized cost is greater than fair value to be considered as other-than-temporary	6 months
Minimum outstanding impaired commercial loans	$ 2,500,000
Liability for credit losses on lending-related commitments	$ 55,000,000	$ 56,000,000	$ 35,000,000	$ 37,000,000
Minimum percentage for an input to be significant of the total fair value of a particular asset or liability	10.00%
Threshold percentage by which amortized cost is greater than fair value to be considered as other-than-temporary	20.00%
Percentage of principal investment in other investments	25.00%	46.00%
Fair value of principal investments held in private companies	$ 185,000,000	$ 304,000,000
Accumulated depreciation and amortization on premises and equipment, total	1,600,000,000	1,400,000,000
Internally developed software, net of accumulated amortization	$ 69,000,000	77,000,000
Capitalized computer software amortization, maximum period allowable	5 years
Amortization period of stock-based compensation awards	5 years
Vesting period for compensation cost	4 years
Stock Options [Member]
Accounting Policies [Line Items]
Options expiration years	10 years
Stock Options [Member] | One year after the grant date [Member]
Accounting Policies [Line Items]
Rate at which employee stock options granted to be exercisable	25.00%
Allowance for Loans and Leases Receivable [Member]
Accounting Policies [Line Items]
Liability for credit losses on lending-related commitments	$ 55,000,000	56,000,000
RE Commercial [Member]
Accounting Policies [Line Items]
Fair value at end of year	356,000,000	321,000,000
Residential Mortgage Backed Securities [Member]
Accounting Policies [Line Items]
Fair value at end of year	$ 33,000,000	$ 28,000,000
Minimum [Member]
Accounting Policies [Line Items]
Intangible assets useful life (in years)	6 months
Maximum [Member]
Accounting Policies [Line Items]
Nonperforming loans, collectively evaluated for impairment	$ 2,500,000
Intangible assets useful life (in years)	20 years
Series A Preferred Stock [Member]
Accounting Policies [Line Items]
Preferred stock, dividend rate, percentage	7.75%