Fair Value Measurements - Additional Information (Detail) (USD $)	1 Months Ended	3 Months Ended	6 Months Ended
	Apr. 30, 2014	Mar. 31, 2014	Jun. 30, 2014	Jun. 30, 2013	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available for sale securities portfolio, value			$ 29,689,400,000		$ 28,392,800,000
Trading account securities			2,700,000		1,700,000
Settlement of contingent consideration	55,300,000	55,300,000
Transfers into Level 3 assets			0	0
Transfers out of Level 3 assets			0	0
Transfers into Level 3 liabilities			0	0
Transfers out of Level 3 liabilities			0	0
Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Number of available for sale securities portfolio			837		831
Available for sale securities portfolio, value			27,200,000,000		26,400,000,000
Loans | Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Financial Instrument, fair value			16,900,000	45,600,000
Other Real Estate Owned | Level 3
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Financial Instrument, fair value			1,400,000	2,900,000
External Pricing | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Number of available for sale securities portfolio			837		829
Available for sale securities portfolio, value					26,300,000,000
Trading account securities			2,700,000		1,700,000
Internal Pricing | Level 2
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Number of available for sale securities portfolio					2
Available for sale securities portfolio, value					$ 57,400,000