Variable Interest Entities - Additional Information (Detail)	1 Months Ended	12 Months Ended
	Jun. 30, 2015 USD ($) Investment	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Variable Interest Entity [Line Items]
Investment using net asset value per share		$ 45,800,000
Unfunded commitment related to seed capital investments		25,000,000
Pre tax charge		318,100,000	$ (86,100,000)	$ (176,900,000)
Tax Credit Structures
Variable Interest Entity [Line Items]
Carrying amounts		173,500,000	208,900,000
Exposure to loss from liquidity arrangements and obligations to purchase assets		0
Liabilities related to unfunded commitments		10,500,000	15,600,000
Affordable housing tax credits and other tax benefits		52,500,000	58,100,000
Leveraged Leasing Transactions
Variable Interest Entity [Line Items]
Carrying amounts		389,400,000	$ 547,600,000
Exposure to loss from liquidity arrangements and obligations to purchase assets		$ 0
Leveraged Leasing Transactions | Lower Limit
Variable Interest Entity [Line Items]
Funding of asset's cost via an equity interest		20.00%
Funding of asset's cost via third party non recourse debt holders		70.00%
Leveraged Leasing Transactions | Upper Limit
Variable Interest Entity [Line Items]
Funding of asset's cost via an equity interest		30.00%
Funding of asset's cost via third party non recourse debt holders		80.00%
Investment Funds
Variable Interest Entity [Line Items]
Exposure to loss from liquidity arrangements and obligations to purchase assets		$ 0
Cash contribution	$ 45,800,000
Number of constant-dollar NAV investment funds contributions were made | Investment	4
Constant Dollar Net Asset Value Investment Funds [Member] | Investment Funds
Variable Interest Entity [Line Items]
Net assets held by fund	$ 1.00
Pre tax charge	$ 45,800,000
Other Assets
Variable Interest Entity [Line Items]
Investment using net asset value per share		$ 25,300,000