Investments - Summary of Fair Value, Including Financial Guarantee, and Weighted-Average Underlying Rating, Excluding Financial Guarantee, of Insured Securities (Phantom) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Investment [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities	$ (7)	$ 0
Investment expense	(2)	(1)	$ (4)	$ (4)
Securities available-for-sale and short-term	17	15	44	59
Net investment income (loss)	11	21	(6)	112
Gains (losses) on securities held as of reporting date [Member]
Investment [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities			(49)	16
Other Investments Income	(6)	(1)	(22)	14
Fixed Income Investments [Member]
Investment [Line Items]
Gross Investment Income, Operating	16	16	45	63
Short-Term [Member]
Investment [Line Items]
Gross Investment Income, Operating	3	0	4	0
Other Investments [Member]
Investment [Line Items]
Gross Investment Income, Operating	$ (5)	$ 6	$ (28)	$ 53