Number of banking offices acquired.

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Number of shares of equity interests issued or issuable to acquire entity.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

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Amount of intangible assets, excluding goodwill, acquired at the acquisition date.

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For transactions that are recognized separately from the acquisition of assets and assumptions of liabilities in the business combination, such as related to pre-existing relationships with the acquiree, this element represents the disclosure of the amount of acquisition related costs which have been expensed.

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This item represents an other than temporary decline in value that has been recognized against an investment accounted for under the equity method of accounting. The excess of the carrying amount over the fair value of the investment represents the amount of the write down which is or was reflected in earnings. The written down value is a new cost basis with the adjusted value of the investment becoming its new carrying value subject to the equity accounting method. Evidence of a loss in value might include, but would not necessarily be limited to, absence of an ability to recover the carrying amount of the investment or inability of the investee to sustain an earnings capacity which would justify the carrying amount of the investment.

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Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price.

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The cash inflow associated with the sale of debt and equity securities classified as available-for-sale securities.

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The cash outflow during the period from the repayment of aggregate short-term and long-term debt. Excludes payment of capital lease obligations.

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Acquisitions - Additional Information (Detail)		1 Months Ended	3 Months Ended		9 Months Ended
Acquisitions - Additional Information (Detail)	Nov. 01, 2015 USD ($) Office shares	Nov. 30, 2015 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)
Business Acquisition [Line Items]
Proceeds from sales of investment securities					$ 61,947,000	$ 2,579,000
Goodwill			$ 4,593,112,000		$ 4,593,112,000		$ 4,593,112,000
Hudson City [Member]
Business Acquisition [Line Items]
Number of banking offices acquired in New Jersey, Connecticut and New York \| Office	135
Gross amount of cash paid in the acquisition	$ 2,064,284,000
Business acquisition, purchase price	5,203,108,000
Proceeds from sales of investment securities		$ 5,800,000,000
Repayments of borrowings assumed in acquisition		$ 10,600,000,000
Goodwill	1,079,787,000
Core deposit intangible	$ 131,665,000
Amortization period of core deposit intangible					7 years
Other- than-temporary impairment				$ 23,000,000		97,000,000
Merger-related expenses			$ 0	$ 0	$ 35,755,000	$ 0
Hudson City [Member] \| Common Stock [Member]
Business Acquisition [Line Items]
Shares issued upon acquisition \| shares	25,953,950