Share Capital - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended	6 Months Ended
	Jul. 07, 2017	Jun. 30, 2017	Jun. 30, 2017	Feb. 17, 2017	May 13, 2016
Shareholders Equity Disclosure [Line Items]
Share repurchase program, number of shares repurchased and retired in the period		6,000,000	11,100,000
Share repurchase program, value of shares repurchased and retired during the period		$ 250.1	$ 450.6
Minimum
Stock plans
Award vesting period			3 years
Maximum
Stock plans
Award vesting period			4 years
Settling of employee withholding taxes
Shareholders Equity Disclosure [Line Items]
Share repurchase program, value of shares repurchased and retired during the period		$ 0.1	$ 0.6
Stock options
Stock plans
Options granted (in shares)			900,000
Options, weighted average grant date fair value, per share			$ 6.74
Restricted Stock [Member]
Stock plans
Other awards granted during the period (in shares)			34,650
Aggregate grant date fair value			$ 1.5
Restricted stock units
Stock plans
Other awards granted during the period (in shares)			1,100,000
Aggregate grant date fair value			$ 43.4
Restricted stock units | Three Year Option
Stock plans
Award vesting period			3 years
Restricted stock units | Four Year Option
Stock plans
Award vesting period			4 years
Liability-classed cash units
Stock plans
Other awards granted during the period (in shares)			600,000
Aggregate grant date fair value			$ 22.6
Liability-classed cash units | Three Year Option
Stock plans
Award vesting period			3 years
Liability-classed cash units | Four Year Option
Stock plans
Award vesting period			4 years
Performance Shares
Stock plans
Other awards granted during the period (in shares)			600,000
Aggregate grant date fair value			$ 24.6
Maximum number of performance shares			1,200,000
Performance Shares | Minimum
Stock plans
Pinal payout percentage			0.00%
Performance Shares | Maximum
Stock plans
Pinal payout percentage			200.00%
May 2016 Program
Shareholders Equity Disclosure [Line Items]
Share repurchase program, authorized amount					$ 1,000.0
Share repurchase program, number of shares repurchased and retired in the period			2,600,000
Share repurchase program, value of shares repurchased and retired during the period			$ 100.0
Share repurchase program, remaining authorization				$ 349.0
February 2017 Program
Shareholders Equity Disclosure [Line Items]
Share repurchase program, authorized amount				$ 1,000.0
Share repurchase program, number of shares repurchased and retired in the period		6,000,000	8,500,000
Share repurchase program, value of shares repurchased and retired during the period		$ 250.0	$ 350.0
Share repurchase program, remaining authorization		$ 650.0	$ 650.0
Series D Preferred Stock [Member] | Subsequent Event [Member]
Shareholders Equity Disclosure [Line Items]
Share repurchase program, number of shares repurchased and retired in the period	27,205
Payments for Repurchase of Preferred Stock and Preference Stock	$ 25.8
Preferred Stock Redemption Discount	1.3
Preferred Stock, Value, Outstanding	$ 27.1
Series E Preferred Stock | Subsequent Event [Member]
Shareholders Equity Disclosure [Line Items]
Share repurchase program, number of shares repurchased and retired in the period	329,722
Payments for Repurchase of Preferred Stock and Preference Stock	$ 310.6
Preferred Stock Redemption Discount	13.8
Preferred Stock, Value, Outstanding	$ 324.4
Noncumulative perpetual preferred shares | Subsequent Event [Member]
Shareholders Equity Disclosure [Line Items]
Share repurchase program, number of shares repurchased and retired in the period	46,635
Payments for Repurchase of Preferred Stock and Preference Stock	$ 45.6
Preferred Stock Redemption Premium	(1.9)
Preferred Stock, Value, Outstanding	$ 43.7