Share Capital - Narrative (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions			6 Months Ended		12 Months Ended
	Apr. 01, 2021	Jan. 04, 2021	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2019	Dec. 31, 2020
Class of Stock [Line Items]
Preferred stock par value (in usd per share)			$ 0.20			$ 0.20
Liquidation preference per share (in usd per share)			$ 1,000			$ 1,000
Preferred shares lock-up period			5 years
Immediate payment applied from collateral already paid			$ 309.4	$ 190.6
Forward contract
Class of Stock [Line Items]
Common shares purchased (shares)					25.8
Derivative liability			0.0			$ 309.0
Net collateral paid balance			$ 0.0			$ 104.1
OppenheimerFunds
Class of Stock [Line Items]
Preferred stock par value (in usd per share)			$ 0.20
Liquidation preference per share (in usd per share)			$ 1,000
Preferred shares dividend rate (percent)			5.90%
Forward Contract, $200 Million, Entered On May 13th, 2019 | Forward contract
Class of Stock [Line Items]
Immediate payment applied from collateral already paid		$ 117.0
Forward Contract, $200 Million, Entered On July 2nd, 2019 | Forward contract
Class of Stock [Line Items]
Immediate payment applied from collateral already paid	$ 120.0
Forward Contract, $100 Million, Entered On August 27th, 2019 | Forward contract
Class of Stock [Line Items]
Immediate payment applied from collateral already paid	$ 72.3