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		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Investment [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities	$ (29)	$ 9
Investment expense	(1)	(1)	$ (3)	$ (3)
Securities available-for-sale and short-term	13	22	27	44
Net investment income (loss)	(21)	42	(16)	91
Gains (losses) on securities held as of reporting date [Member]
Investment [Line Items]
Net Realized and Unrealized Gain (Loss) on Trading Securities			(42)	16
Other Investments Income	(15)	8	(17)	15
Fixed Income Investments [Member]
Investment [Line Items]
Gross Investment Income, Operating	13	23	28	46
Short-Term [Member]
Investment [Line Items]
Gross Investment Income, Operating	1	0	1	0
Other Investments [Member]
Investment [Line Items]
Gross Investment Income, Operating	$ (23)	$ 20	$ (23)	$ 47