Pension and Postretirement Benefit Plans and Defined Contribution Plans - Long-term Target Asset Allocations Ranges and the Percentage of the Fair Value of Plan Assets (Detail)	Dec. 31, 2020	Dec. 31, 2019
US [Member] | Pension Plan [Member] | Qualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity and debt securities, target allocation percentage	100.00%
Equity and debt securities, percentage of plan assets	100.00%	100.00%
US [Member] | Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity and debt securities, target allocation percentage	100.00%
Equity and debt securities, percentage of plan assets	100.00%	100.00%
US [Member] | Cash and Cash Equivalents [Member] | Pension Plan [Member] | Qualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity and debt securities, percentage of plan assets	4.90%	2.50%
US [Member] | Cash and Cash Equivalents [Member] | Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity and debt securities, percentage of plan assets	0.00%	0.00%
US [Member] | Equity Securities [Member] | Pension Plan [Member] | Qualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity and debt securities, percentage of plan assets	28.40%	31.80%
US [Member] | Fixed Income Securities [Member] | Pension Plan [Member] | Qualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity and debt securities, percentage of plan assets	50.20%	48.70%
US [Member] | Other Investments [Member] | Pension Plan [Member] | Qualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity and debt securities, percentage of plan assets	16.60%	17.00%
US [Member] | Other Investments [Member] | Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity and debt securities, percentage of plan assets	100.00%	100.00%
International [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity and debt securities, target allocation percentage	100.00%
Equity and debt securities, percentage of plan assets	100.00%	100.00%
International [Member] | Cash and Cash Equivalents [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity and debt securities, percentage of plan assets	4.20%	2.50%
International [Member] | Equity Securities [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity and debt securities, percentage of plan assets	20.90%	21.50%
International [Member] | Fixed Income Securities [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity and debt securities, percentage of plan assets	48.40%	46.90%
International [Member] | Other Investments [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity and debt securities, percentage of plan assets	26.60%	29.20%
Minimum [Member] | US [Member] | Cash and Cash Equivalents [Member] | Pension Plan [Member] | Qualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity and debt securities, target allocation percentage	0.00%
Minimum [Member] | US [Member] | Cash and Cash Equivalents [Member] | Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity and debt securities, target allocation percentage	0.00%
Minimum [Member] | US [Member] | Equity Securities [Member] | Pension Plan [Member] | Qualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity and debt securities, target allocation percentage	35.00%
Minimum [Member] | US [Member] | Fixed Income Securities [Member] | Pension Plan [Member] | Qualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity and debt securities, target allocation percentage	28.00%
Minimum [Member] | US [Member] | Other Investments [Member] | Pension Plan [Member] | Qualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity and debt securities, target allocation percentage	5.00%
Minimum [Member] | US [Member] | Other Investments [Member] | Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity and debt securities, target allocation percentage	95.00%
Minimum [Member] | International [Member] | Cash and Cash Equivalents [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity and debt securities, target allocation percentage	0.00%
Minimum [Member] | International [Member] | Equity Securities [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity and debt securities, target allocation percentage	20.00%
Minimum [Member] | International [Member] | Fixed Income Securities [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity and debt securities, target allocation percentage	35.00%
Minimum [Member] | International [Member] | Other Investments [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity and debt securities, target allocation percentage	10.00%
Maximum [Member] | US [Member] | Cash and Cash Equivalents [Member] | Pension Plan [Member] | Qualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity and debt securities, target allocation percentage	10.00%
Maximum [Member] | US [Member] | Cash and Cash Equivalents [Member] | Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity and debt securities, target allocation percentage	5.00%
Maximum [Member] | US [Member] | Equity Securities [Member] | Pension Plan [Member] | Qualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity and debt securities, target allocation percentage	55.00%
Maximum [Member] | US [Member] | Fixed Income Securities [Member] | Pension Plan [Member] | Qualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity and debt securities, target allocation percentage	53.00%
Maximum [Member] | US [Member] | Other Investments [Member] | Pension Plan [Member] | Qualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity and debt securities, target allocation percentage	20.00%
Maximum [Member] | US [Member] | Other Investments [Member] | Postretirement Benefits Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity and debt securities, target allocation percentage	100.00%
Maximum [Member] | International [Member] | Cash and Cash Equivalents [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity and debt securities, target allocation percentage	10.00%
Maximum [Member] | International [Member] | Equity Securities [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity and debt securities, target allocation percentage	40.00%
Maximum [Member] | International [Member] | Fixed Income Securities [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity and debt securities, target allocation percentage	60.00%
Maximum [Member] | International [Member] | Other Investments [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Equity and debt securities, target allocation percentage	35.00%