Pension Plans and Other Postretirement Benefits - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Minimum pension liability	$ 413,168,000
Minimum pension liability adjustment net of tax		$ 304,546,000
Decrease in minimum liability adjustment		36,749,000
Defined contribution pension and retirement savings plans total expense	$ 30,000,000	25,000,000	$ 23,000,000
Assumptions used calculating net periodic benefit sensitivity rate increase decrease discount rate	0.25%
Effect of 25 basis point increase in rate of return on pension expense	$ 4,000,000
Effect of 25 basis point decrease in rate of return on pension expense	7,000,000
Effect of 25 basis point decrease in discount rate on benefit obligation	76,000,000
Effect of 25 basis point increase in discount rate on benefit obligation	$ 80,000,000
Annual rate of increase in health care cost assumed for next fiscal year	6.50%
Defined Benefit Plan, ultimate health care cost trend rate	5.00%
Period for decreasing the annual rate	over 11 years
Defined benefit pension plans	$ 304,463,000
Percentage of total assets	15.00%
Defined benefit plan fair value of plan assets	$ 2,013,117,000	1,640,300,000
Qualified benefit pension plans		0	0
Percentage of pension plan assets that is not exceeded by investment in security of single Non-US Government of Government agency	10.00%
Percentage of eligible employees contribution for Retirement Savings Plan	50.00%
Percentage of employer matching contribution to employee's contribution	75.00%
Maximum employer contribution on Employee's qualified contribution	4.50%
Qualified defined contribution plans expense during the period	$ 38,229,000	36,766,000	34,145,000
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	$ 1,019,639,000	920,077,000
Equity Securities [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocations for plan assets	25.00%
Equity Securities [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocations for plan assets	60.00%
Total Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	$ 571,367,000	445,698,000
Total Debt Securities [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocations for plan assets	10.00%
Total Debt Securities [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocations for plan assets	65.00%
Other Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	$ 304,463,000	234,969,000
Other Securities [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocations for plan assets	10.00%
Other Securities [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Target allocations for plan assets	85.00%
M&T Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan fair value of plan assets	$ 154,818,000	$ 164,474,000
Percentage of common stock in total plan assets	7.70%	10.00%
Supplemental Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$ 165,210,000	$ 160,433,000
Accumulated benefit obligation	165,210,000	160,433,000
Employer contributions	11,444,000	10,772,000
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	2,188,736,000	2,007,158,000	2,004,531,000
Accumulated benefit obligation	2,158,601,000	1,979,225,000
Minimum pension liability	463,570,000
Defined benefit plan fair value of plan assets	2,014,891,000	1,642,131,000	1,625,134,000
Employer contributions	211,444,000	10,772,000
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	68,637,000	109,922,000	$ 121,497,000
Minimum pension liability	50,402,000
Employer contributions	$ 7,574,000	$ 7,588,000