Offsetting Assets and Liabilities - Offsetting of Derivative Liabilities (Detail) - USD ($)	Dec. 31, 2021	Dec. 31, 2020
Derivatives:
Gross amounts of recognized liabilities	$ (2,951,000)	$ (807,000)
Gross Amounts Offset in the Consolidated Balance Sheets	0	0
Net Amounts of Assets (Liabilities) presented in the Consolidated Balance Sheets	(2,951,000)	(807,000)
Gross amounts not offset in the consolidated balance sheets, financial instruments	0	111,000
Gross amounts not offset in the consolidated balance sheets, cash collateral pledged	2,951,000	610,000
Net Amount	0	(86,000)
Repurchase Agreements:
Gross Amounts of Recognized Assets (Liabilities)	(6,987,834,000)	(7,228,699,000)
Gross Amounts Offset in the Consolidated Balance Sheets	0	0
Net Amounts of Assets (Liabilities) presented in the Consolidated Balance Sheets	(6,987,834,000)	(7,228,699,000)
Gross amounts not offset in the consolidated balance sheets, financial instruments	6,987,834,000	7,228,699,000
Gross amounts not offset in the consolidated balance sheets, cash collateral pledged	0	0
Net Amount	0	0
Gross Amounts of Recognized Assets (Liabilities)	(6,990,785,000)	(7,229,506,000)
Gross Amounts Offset in the Consolidated Balance Sheets	0	0
Net Amounts of Assets (Liabilities) presented in the Consolidated Balance Sheets	(6,990,785,000)	(7,229,506,000)
Gross amounts not offset with financial assets (liabilities) in the balance sheets, financial instruments	6,987,834,000	7,228,810,000
Gross amounts not offset with financial assets (liabilities) in the balance sheets, cash collateral (received) pledged	2,951,000	610,000
Net Amount	0	(86,000)
Cash collateral pledged on derivatives	224,400,000	245,000,000
Cash collateral received	280,000	3,546,000
Fair value of securities pledged under repurchase agreements, excluding cash collateral	7,300,000,000	7,600,000,000
Securities sold under agreements to repurchase fair value of collateral	7,329,702,000	7,615,635,000
Cash
Repurchase Agreements:
Securities sold under agreements to repurchase fair value of collateral	3,527,000	700,000
Interest Rate Swaps
Repurchase Agreements:
Cash collateral received	280,000	1,630,000
Repurchase Agreements:
Repurchase Agreements:
Cash collateral received	$ 0	$ 1,916,000