Pension and Other Retirement Benefits - Additional Information (Detail) - Unfunded Plan - United States $ in Millions	3 Months Ended
Mar. 31, 2021 USD ($)
Pension Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Employer contributions	$ 1
Estimated additional payments, remainder of fiscal year	44
Other Retirement Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Estimated additional payments, remainder of fiscal year	$ 1

Amount of contribution received by defined benefit plan from employer which increases plan assets.

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration