Investments - Additional Information (Details) - USD ($)	Sep. 30, 2020	Dec. 31, 2019
Schedule of Investments [Line Items]
Debt Securities, Available-for-sale, Allowance for Credit Loss	$ 0
Securities fair value	7,000,000	$ 6,000,000
Ambac Assurance [Member]
Schedule of Investments [Line Items]
Unsettled Amounts Secured Notes from LSNI	10,000,000	55,000,000
Interest Rate Contract [Member]
Schedule of Investments [Line Items]
Other investments	53,000,000	176,000,000
Reported Value Measurement [Member]
Schedule of Investments [Line Items]
Other investments	60,000,000	136,000,000
Reported Value Measurement [Member] | Interest Rate Contract [Member]
Schedule of Investments [Line Items]
Other investments	3,000,000	$ 81,000,000
Commitments [Member] | Partnership Interest [Member]
Schedule of Investments [Line Items]
Other investments	$ 48,000,000