Pension and Other Retirement Benefits - Additional Information (Detail) $ in Millions	9 Months Ended
Sep. 30, 2021 USD ($)
Unfunded Plan \| Pension Plans \| United States
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Employer contributions	$ 46

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

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration