Debt (Details)	3 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2020 USD ($) financial_institution line_of_credit	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Short-term Debt [Line Items]
Short-term Debt
Commercial Paper
Short-term Debt [Line Items]
Weighted average interest rates on average daily borrowings		1.90%		2.60%
Short-term Debt		$ 104,800,000	$ 0
Weighted average interest rate		2.10%
Debt instrument, term			317 days
Short-term debt, average outstanding amount		$ 44,700,000		$ 438,600,000
Uncommited Lines of Credit
Short-term Debt [Line Items]
Weighted average interest rates	2.00%		1.90%
Short-term Debt	$ 0		$ 0
Short-term debt, average outstanding amount	3,300,000		1,900,000
Line of Credit
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	800,000,000.0
Maximum incremental increase	200,000,000.0
Amount outstanding	0		0
EQH
Short-term Debt [Line Items]
Amount outstanding	$ 830,000,000.0		$ 560,000,000.0
Weighted average interest rates	0.20%		1.60%
Average borrowing period			57 days
Average daily borrowings	$ 592,100,000		$ 358,600,000
Weighted average interest rates on average daily borrowings	1.30%		1.60%
Revolving Credit Facility
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	$ 200,000,000.0
Revolving Credit Facility | EQH
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	900,000,000.0
Revolving Credit Facility | Line of Credit
Short-term Debt [Line Items]
Amount outstanding	$ 0		$ 0
Weighted average interest rates	2.30%		3.20%
Average daily borrowings	$ 23,900,000		$ 23,500,000
Subsidiaries | Line of Credit
Short-term Debt [Line Items]
Line of credit facility, maximum borrowing capacity	$ 175,000,000.0
Number of uncommitted lines of credit | line_of_credit	3
Number of financial institutions offering lines of credit | financial_institution	3
Number of financial institutions with stated limits | line_of_credit	2