Fair Value of Financial Instruments - Changes in Level 3 Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014
Commercial Secured Borrowings
Derivatives
Ending balance	$ 63,152
Liabilities
Beginning balance	66,707	$ 0
Transfer to FVO	0
Acquisitions	0	65,048
Sales	0	0
Principal paydowns	(593)	(374)
Amortization income		0
Gains (losses) in net income, net	(3,011)	2,033
Unrealized gains in OCI, net	0	0
Other settlements, net	49	0
Ending Balance	63,152	66,707
Asset-backed Securities
Assets
Unrealized gains in OCI, net	0
Derivatives
Ending balance	996,820
Liabilities
Beginning balance	0
Transfer to FVO	1,302,216
Acquisitions	0
Sales	(1,362)
Principal paydowns	(312,800)
Gains (losses) in net income, net	8,366
Other settlements, net	400
Ending Balance	996,820	0
Residential Loans at Fair Value
Assets
Beginning balance	1,677,984	391,100
Transfer to FVO	1,370,699
Acquisitions	5,231,532	5,020,988
Sales	(3,857,807)	(3,746,417)
Principal paydowns	(612,473)	(42,657)
Amortization income		0
Gains (losses) in net income, net	(6,071)	56,835
Unrealized gains in OCI, net	0	0
Other settlements, net	(6,313)	(1,865)
Ending Balance	3,797,551	1,677,984
Commercial Loans
Assets
Beginning balance	237,496	89,111
Transfer to FVO	0
Acquisitions	617,519	937,594
Sales	(754,636)	(807,931)
Principal paydowns	(780)	(4,157)
Amortization income		0
Gains (losses) in net income, net	7,199	22,824
Unrealized gains in OCI, net	0	0
Other settlements, net	0	55
Ending Balance	106,798	237,496
Trading Securities
Assets
Beginning balance	111,606	124,555
Transfer to FVO	0
Acquisitions	399,990	81,545
Sales	(83,038)	(64,393)
Principal paydowns	(7,245)	(5,934)
Amortization income		0
Gains (losses) in net income, net	(17,302)	(24,167)
Unrealized gains in OCI, net	0	0
Other settlements, net	0	0
Ending Balance	404,011	111,606
Available-for-sale Securities
Assets
Beginning balance	1,267,624	1,558,306
Transfer to FVO	0
Acquisitions	33,370	237,499
Sales	(366,373)	(440,361)
Principal paydowns	(131,387)	(168,308)
Amortization income		32,774
Gains (losses) in net income, net	72,612	23,412
Unrealized gains in OCI, net	(46,961)	24,302
Other settlements, net	360	0
Ending Balance	829,245	1,267,624
Mortgage Servicing Rights
Assets
Beginning balance	139,293	64,824
Transfer to FVO	0
Acquisitions	95,281	95,550
Sales	(18,206)	0
Principal paydowns	0	0
Amortization income		0
Gains (losses) in net income, net	(24,392)	(21,081)
Unrealized gains in OCI, net	0	0
Other settlements, net	0	0
Ending Balance	191,976	139,293
Derivatives
Ending balance	191,976
Guarantee Asset
Assets
Beginning balance	7,201	0
Transfer to FVO	0
Acquisitions	0	7,201
Sales	0	0
Principal paydowns	0	0
Amortization income		0
Gains (losses) in net income, net	(1,377)	0
Unrealized gains in OCI, net	0	0
Other settlements, net	(127)	0
Ending Balance	5,697	7,201
Derivative Assets
Assets
Beginning balance	1,119
Transfer to FVO	0
Acquisitions	0
Sales	0
Principal paydowns	0
Gains (losses) in net income, net	60,823
Unrealized gains in OCI, net	0
Other settlements, net	(58,734)
Ending Balance	3,208	1,119
Derivatives
Beginning balance	$ 1,119	(379)
Acquisitions		0
Sales		0
Principal paydowns		0
Amortization income		0
Gains (losses) in net income, net		14,527
Unrealized gains in OCI, net		0
Other settlements, net		(13,029)
Ending balance		$ 1,119

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