Shareholders' Equity - Additional Information (Detail)	3 Months Ended
	Jun. 30, 2018 $ / shares	Mar. 31, 2018 USD ($) $ / shares shares	Mar. 31, 2017 USD ($) $ / shares	Dec. 31, 2017 shares
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Repurchase of common shares | $		$ 156,000,000	$ 107,000,000
Cash dividends declared on common shares (in usd per share)		$ 0.105	$ 0.085
Depository Shares, Series D [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Shares issued | $		$ 525,000,000
Series D Preferred Stock [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Dividend payable per share		$ 12.50
Preferred stock, par value (in usd per share)		1
Preferred stock, liquidation preference (in usd per share)		$ 25,000
Preferred stock, shares authorized (in shares) | shares		21,000		21,000
Preferred stock, shares outstanding (in shares) | shares		21,000		21,000
Depository receipt ratio		0.04
Depository Shares, Series E [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Shares issued | $		$ 500,000,000
Series E Preferred Stock [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Dividend payable per share		$ 0.382813
Preferred stock, par value (in usd per share)		1
Preferred stock, liquidation preference (in usd per share)		$ 1,000
Preferred stock, shares authorized (in shares) | shares		500,000		500,000
Preferred stock, shares outstanding (in shares) | shares		500,000		500,000
Depository receipt ratio		0.025
2017 Capital Plan [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Authorized amount of share repurchases | $		$ 800,000,000
Common shares repurchased, value | $		199,000,000
Repurchase of common shares | $		156,000,000
Employee equity compensation program Common Share repurchases | $		$ 43,000,000
Cash dividends declared on common shares (in usd per share)		$ 0.105
Scenario, Forecast [Member] | 2017 Capital Plan [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Proposed increase in cash dividends declared on common shares, per share	$ 0.120