Schedule of Target Assets Allocation (Detail)	Dec. 31, 2019
Barclays Corporate or Better Index | U.S. corporate fixed income
Defined Benefit Plan Disclosure
Target assets allocation percentage	75.00%
MSCI World Minimum Volatility Index | Global equity Securities
Defined Benefit Plan Disclosure
Target assets allocation percentage	5.00%
Barclays Long Government Bond Index | U.S. government fixed income
Defined Benefit Plan Disclosure
Target assets allocation percentage	14.00%
Barclays High Yield Index | High yield fixed income
Defined Benefit Plan Disclosure
Target assets allocation percentage	5.00%
Citigroup Three Month Treasury Bill Index | Cash
Defined Benefit Plan Disclosure
Target assets allocation percentage	1.00%