Shareholders' Equity - Additional Information (Detail)			3 Months Ended				12 Months Ended
	Dec. 12, 2016 USD ($)	Sep. 09, 2016 USD ($)	Dec. 31, 2016 USD ($) $ / shares shares	Sep. 30, 2016 $ / shares	Jun. 30, 2016 $ / shares	Mar. 31, 2016 $ / shares	Dec. 31, 2016 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) $ / shares	Aug. 01, 2016 USD ($)
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Cash dividends declared per common share (in dollars per share) | $ / shares							$ 0.33	$ 0.29	$ 0.250
Preferred stock | $			$ 1,665,000,000				$ 1,665,000,000	$ 290,000,000
Dividends payable | $							(335,000,000)	$ (267,000,000)	$ (240,000,000)
Series A Preferred Stock [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Preferred stock | $			$ 290,000,000				$ 290,000,000
Preferred stock, dividend rate, percentage							7.75%
Preferred stock, par value (in dollars per share) | $ / shares			$ 1				$ 1
Preferred stock, liquidation preference (in dollars per share) | $ / shares			$ 100				$ 100
Preferred stock, shares authorized | shares			7,475,000				7,475,000	7,475,000
Preferred stock, shares outstanding | shares			2,900,234				2,900,234	2,900,234
Dividend payable (in dollars per share) | $ / shares			$ 1.9375				$ 1.9375
Dividends payable | $							$ (22,000,000)
Series C Preferred Stock [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Preferred stock | $										$ 350,000,000
Preferred stock, par value (in dollars per share) | $ / shares			1				$ 1
Preferred stock, liquidation preference (in dollars per share) | $ / shares			$ 25				$ 25
Preferred stock, shares authorized | shares			14,000,000				14,000,000
Preferred stock, shares outstanding | shares			14,000,000				14,000,000
Dividend payable (in dollars per share) | $ / shares			$ 0.539063				$ 0.539063
Dividends payable | $			$ (8,000,000)
Depository Shares [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Shares issued | $	$ 500,000,000	$ 525,000,000
Series D Preferred Stock [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Preferred stock, par value (in dollars per share) | $ / shares			$ 1				1
Preferred stock, liquidation preference (in dollars per share) | $ / shares			$ 25,000				$ 25,000
Preferred stock, shares authorized | shares			21,000				21,000
Preferred stock, shares outstanding | shares			21,000				21,000
Dividend payable (in dollars per share) | $ / shares			$ 13.33				$ 13.33
Dividends payable | $			$ (7,000,000)
Entity Listing, Depository Receipt Ratio		0.04
Series E Preferred Stock [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Preferred stock, par value (in dollars per share) | $ / shares			$ 1				1
Preferred stock, liquidation preference (in dollars per share) | $ / shares			$ 1,000				$ 1,000
Preferred stock, shares authorized | shares			500,000				500,000
Preferred stock, shares outstanding | shares			500,000				500,000
Entity Listing, Depository Receipt Ratio	0.025
2016 Capital Plan [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Stock repurchase program authorized amount | $			$ 350,000,000				$ 350,000,000
Repurchase of common stock | $							$ 133,000,000
2016 [Member] | 2016 Capital Plan [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Cash dividends declared per common share (in dollars per share) | $ / shares			$ 0.085	$ 0.085	$ 0.085	$ 0.075
2017 [Member] | 2016 Capital Plan [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Proposed increase in cash dividends declared on common shares (in dollars per share) | $ / shares							$ 0.095
Retained Earnings [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Dividends, preferred stock, cash | $									$ 22,000,000
Retained Earnings [Member] | Series A Preferred Stock [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Dividends, preferred stock, cash | $							$ 22,000,000	$ 23,000,000
Retained Earnings [Member] | Series C Preferred Stock [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Dividends, preferred stock, cash | $							8,000,000
Retained Earnings [Member] | Series D Preferred Stock [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Dividends, preferred stock, cash | $							$ 7,000,000