Shareholders' Equity (Details) - USD ($) $ / shares in Units, shares in Millions							3 Months Ended		9 Months Ended
	Sep. 29, 2017	Sep. 15, 2017	Jun. 30, 2017	Jun. 15, 2017	Mar. 31, 2017	Mar. 15, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Aug. 02, 2017
Class of Stock [Line Items]
Dividends per common share (in dollars per share)							$ 0.32	$ 0.31	$ 0.96	$ 0.93
Dividends declared and paid, Preference shares							$ 5,595,000	$ 5,595,000	$ 16,786,000	$ 16,786,000
Retained Earnings
Class of Stock [Line Items]
Dividends declared and paid, Preference shares									16,786,000	16,786,000
Dividends declared and paid, Common shares									$ 38,624,000	$ 38,886,000
Common Shares
Class of Stock [Line Items]
Dividends per common share (in dollars per share)		$ 0.32		$ 0.32		$ 0.32
Dividends paid per common share (in dollars per share)	$ 0.32		$ 0.32		$ 0.32
Share repurchase program, Authorized amount											$ 500,000,000
Common shares repurchased during period, Number of shares (in shares)									1.3
Common shares repurchased during period, Aggregate amount									$ 188,600,000
Common shares repurchased during period, Average cost (in dollars per share)									$ 142.67
Share repurchase program, Remaining authorized aggregate amount							$ 467,300,000		$ 467,300,000
Series C Preference Shares
Class of Stock [Line Items]
Dividend rate, percentage									6.08%
Liquidation preference per annum (in dollars per share)							$ 1.52		$ 1.52
Liquidation preference quarterly (in dollars per share)							0.38		$ 0.38
Series E Preference Shares
Class of Stock [Line Items]
Dividend rate, percentage									5.375%
Liquidation preference per annum (in dollars per share)							1.34375		$ 1.34375
Liquidation preference quarterly (in dollars per share)							$ 0.3359375		$ 0.3359375