Income Taxes - Expiration Dates of NOLs and Other Tax Credit Carryforwards Before Valuation Allowances (Detail) $ in Millions	Sep. 30, 2021 USD ($)
Significant Tax Attributes And Dates Of Expiration [Line Items]
NOLs	$ 1,265
Credits	118
2022 - 2028 [Member]
Significant Tax Attributes And Dates Of Expiration [Line Items]
NOLs	229
Credits	28
2029 and Thereafter [Member]
Significant Tax Attributes And Dates Of Expiration [Line Items]
NOLs	218
Credits	88
Indefinite Carryforwards [Member]
Significant Tax Attributes And Dates Of Expiration [Line Items]
NOLs	818
Credits	$ 2