Income Taxes - Expiration of Tax Credit Carryforwards (Detail) $ in Millions	Dec. 31, 2019 USD ($)
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	$ 500
2019 Tax Loss Carryforwards
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	500
2020 Tax Loss Carryforwards
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	16
2021 Tax Loss Carryforwards
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	1
2022 Tax Loss Carryforwards
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	11
2023 Tax Loss Carryforwards
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	10
2024 Tax Loss Carryforwards
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	10
2025-2029 Tax Loss Carryforwards
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	112
Later Tax Loss Carryforwards
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	286
Unlimited Tax Loss Carryforwards
Tax Credit Carryforward [Line Items]
Tax credit carryforwards	$ 54