Share Capital - Narrative (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions			3 Months Ended
	Jan. 04, 2021	May 24, 2019	Mar. 31, 2021	Mar. 31, 2020	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
Common shares outstanding (shares)			461.5		459.1
Common stock lock-up period		2 years
Immediate payment applied from collateral already paid			$ 117.0	$ 190.6
MassMutual | Investor
Class of Stock [Line Items]
Common shares outstanding (shares)			75.6
Forward contract
Class of Stock [Line Items]
Net collateral paid balance			$ 182.9		$ 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