Shareholders' Equity - Preferred shares (Details) - USD ($) $ / shares in Units, $ in Thousands, shares in Millions		1 Months Ended		4 Months Ended	12 Months Ended
	Sep. 29, 2016	Nov. 30, 2017	Aug. 31, 2017	Nov. 30, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Class of Stock [Line Items]
Non-cumulative preferred shares					$ 780,000	$ 780,000
Preferred shares, par value per share					$ 0.01
Proceeds on issuance of preference shares					$ 0	$ 0	$ 319,694
Average cost per share					$ 25.96	$ 26.78	$ 0
Aggregate cost of share repurchase					$ 0	$ 92,555	$ 230,000
Series C Preferred Shares
Class of Stock [Line Items]
Preferred shares, dividend rate (as a percent)						6.75%
Preferred shares, redemption price per share						$ 25
Series E preferred shares
Class of Stock [Line Items]
Non-cumulative preferred shares	$ 450,000
Preferred shares, dividend rate (as a percent)	5.25%
Preferred shares, par value per share	$ 0.01
Liquidation preference per share	25,000
Preferred shares, redemption price per share	$ 25,000
Series E depositary share equivalent
Class of Stock [Line Items]
Preference shares, number of shares issued	18.0
Proportionate interest of preference shares, per depositary share	0.10%
Liquidation preference per share	$ 25
Preferred shares, redemption price per share	$ 25
Series F Preferred Shares
Class of Stock [Line Items]
Preferred shares issued		$ 100,000	$ 230,000	$ 330,000
Preferred shares, dividend rate (as a percent)				5.45%
Preferred shares, par value per share		$ 0.01		$ 0.01
Liquidation preference per share		25,000		25,000
Preferred shares, redemption price per share		$ 25,000		$ 25,000
Series F depositary share equivalent
Class of Stock [Line Items]
Preference shares, number of shares issued		13.2		13.2
Proportionate interest of preference shares, per depositary share		0.10%		0.10%
Liquidation preference per share		$ 25		$ 25
Preferred shares, redemption price per share		$ 25		$ 25