Shareholders' Equity (Details) - USD ($) $ / shares in Units, shares in Thousands			3 Months Ended
	Mar. 31, 2017	Mar. 15, 2016	Mar. 31, 2017	Mar. 31, 2016	Aug. 02, 2016
Class of Stock [Line Items]
Dividends declared per common share (in usd per share)			$ 0.32	$ 0.31
Dividends declared and paid, Preference shares			$ 5,595,000	$ 5,595,000
Retained Earnings
Class of Stock [Line Items]
Dividends declared and paid, Preference shares			5,595,000	5,595,000
Dividends declared and paid, Common shares			$ 13,027,000	$ 13,285,000
Common Shares
Class of Stock [Line Items]
Dividends declared per common share (in usd per share)		$ 0.32
Dividends paid per common share (in usd per share)	$ 0.32
Share repurchase program, Authorized amount (up to)					$ 500,000,000
Common shares repurchased during period, Number of shares (in shares)			550
Common shares repurchased during period, Aggregate amount			$ 80,000,000
Common shares repurchased during period, Average cost (in usd per share)			$ 145.36
Share repurchase program, Remaining authorized aggregate amount	$ 460,000,000		$ 460,000,000