Derivative contract (Detail) - Not Designated as Hedging Instrument [Member] - Equity Index Put Options [Member] - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Derivative [Line Items]
Derivative contract liabilities	$ 286	$ 1,065
Notional value	8,251	10,991
Intrinsic value	$ 83	$ 727
Weighted average remaining life (in years)	7 months 6 days	1 year 2 months 12 days