Employee Benefit Plans - Fair Value of Assets in Qualified Plans (Detail) - Pension Plans [Member] - Qualified Plan [Member]	Dec. 31, 2019	Dec. 31, 2018
People's Qualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	100.00%	100.00%
First Connecticut Qualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	100.00%	100.00%
United Financial Qualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	100.00%
Equity Securities [Member] | People's Qualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	66.00%	70.00%
Equity Securities [Member] | First Connecticut Qualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	66.00%	73.00%
Equity Securities [Member] | United Financial Qualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	9.00%
Cash Equivalents and Fixed Income Securities [Member] | People's Qualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	34.00%	30.00%
Cash Equivalents and Fixed Income Securities [Member] | First Connecticut Qualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	34.00%	27.00%
Cash Equivalents and Fixed Income Securities [Member] | United Financial Qualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Plan assets	91.00%