Fair Value Measurement- Details of Certain Items Measured at Fair Value on Recurring Basis (Detail) (Fair Value, Measurements, Recurring, USD $) In Millions, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Non-agency RMBS
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	$ 920	[1]	$ 953	[1]
Non-agency RMBS | 2007
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	76	[1]	78	[1]
Non-agency RMBS | 2006
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	134	[1]	138	[1]
Non-agency RMBS | 2005
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	276	[1]	284	[1]
Non-agency RMBS | 2004 and earlier
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	434	[1]	453	[1]
Commercial MBS | Domestic
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	1,784	[1]	1,887	[1]
Commercial MBS | 2009-2015 | Domestic
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	686	[1]	639	[1]
Commercial MBS | 2008 | Domestic
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	19	[1]	19	[1]
Commercial MBS | 2007 | Domestic
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	349	[1]	353	[1]
Commercial MBS | 2006 | Domestic
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	545	[1]	599	[1]
Commercial MBS | 2005 | Domestic
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	179	[1]	271	[1]
Commercial MBS | 2004 and earlier | Domestic
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	6	[1]	6	[1]
Foreign covered bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	2,808	[1]	2,868	[1]
Foreign covered bonds | Canada
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	1,394	[1]	1,266	[1]
Foreign covered bonds | United Kingdom
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	604	[1]	690	[1]
Foreign covered bonds | Netherlands
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	215	[1]	244	[1]
Foreign covered bonds | Other
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	595	[1]	668	[1]
Sovereign debt/sovereign guaranteed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	15,243	[1]	17,284	[1]
Sovereign debt/sovereign guaranteed | United Kingdom
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	2,858	[1]	5,076	[1]
Sovereign debt/sovereign guaranteed | France
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	4,252	[1]	3,550	[1]
Sovereign debt/sovereign guaranteed | Netherlands
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	1,237	[1]	1,800	[1]
Sovereign debt/sovereign guaranteed | BELGIUM
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	1,058	[1]	829	[1]
Sovereign debt/sovereign guaranteed | Ireland
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	802	[1]	672	[1]
Sovereign debt/sovereign guaranteed | Spain
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	1,817	[1]	1,978	[1]
Sovereign debt/sovereign guaranteed | Germany
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	1,548	[1]	1,522	[1]
Sovereign debt/sovereign guaranteed | Italy
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	1,252	[1]	1,427	[1]
Sovereign debt/sovereign guaranteed | Other
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	419	[1]	430	[1]
Alt-A RMBS
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	2,138	[1],[2]	2,214	[1],[2]
Alt-A RMBS | 2007
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	599	[1],[2]	620	[1],[2]
Alt-A RMBS | 2006
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	627	[1],[2]	653	[1],[2]
Alt-A RMBS | 2005
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	706	[1],[2]	727	[1],[2]
Alt-A RMBS | 2004 and earlier
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	206	[1],[2]	214	[1],[2]
Securities available-for-sale | European floating rate notes
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	1,452	[1]	1,637	[1]
Securities available-for-sale | European floating rate notes | United Kingdom
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	1,052	[1]	1,172	[1]
Securities available-for-sale | European floating rate notes | Netherlands
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	250	[1]	296	[1]
Securities available-for-sale | European floating rate notes | Ireland
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	129	[1]	144	[1]
Securities available-for-sale | European floating rate notes | Other
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Available-for-sale	$ 21	[1]	$ 25	[1]
Ratings, AAA/AA- | Non-agency RMBS
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	1.00%		1.00%
Ratings, AAA/AA- | Non-agency RMBS | 2004 and earlier
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	3.00%		3.00%
Ratings, AAA/AA- | Commercial MBS | Domestic
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	81.00%		82.00%
Ratings, AAA/AA- | Commercial MBS | 2009-2015 | Domestic
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	84.00%		83.00%
Ratings, AAA/AA- | Commercial MBS | 2008 | Domestic
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	100.00%		100.00%
Ratings, AAA/AA- | Commercial MBS | 2007 | Domestic
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	65.00%		65.00%
Ratings, AAA/AA- | Commercial MBS | 2006 | Domestic
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	82.00%		83.00%
Ratings, AAA/AA- | Commercial MBS | 2005 | Domestic
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	100.00%		100.00%
Ratings, AAA/AA- | Commercial MBS | 2004 and earlier | Domestic
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	100.00%		100.00%
Ratings, AAA/AA- | Foreign covered bonds
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	100.00%		100.00%
Ratings, AAA/AA- | Foreign covered bonds | Canada
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	100.00%		100.00%
Ratings, AAA/AA- | Foreign covered bonds | United Kingdom
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	100.00%		100.00%
Ratings, AAA/AA- | Foreign covered bonds | Netherlands
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	100.00%		100.00%
Ratings, AAA/AA- | Foreign covered bonds | Other
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	100.00%		100.00%
Ratings, AAA/AA- | Sovereign debt/sovereign guaranteed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	74.00%		76.00%
Ratings, AAA/AA- | Sovereign debt/sovereign guaranteed | United Kingdom
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	100.00%		100.00%
Ratings, AAA/AA- | Sovereign debt/sovereign guaranteed | France
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	100.00%		100.00%
Ratings, AAA/AA- | Sovereign debt/sovereign guaranteed | Netherlands
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	100.00%		100.00%
Ratings, AAA/AA- | Sovereign debt/sovereign guaranteed | BELGIUM
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	100.00%		100.00%
Ratings, AAA/AA- | Sovereign debt/sovereign guaranteed | Germany
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	100.00%		100.00%
Ratings, AAA/AA- | Sovereign debt/sovereign guaranteed | Other
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	83.00%		81.00%
Ratings, AAA/AA- | Securities available-for-sale | European floating rate notes
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	79.00%		79.00%
Ratings, AAA/AA- | Securities available-for-sale | European floating rate notes | United Kingdom
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	83.00%		83.00%
Ratings, AAA/AA- | Securities available-for-sale | European floating rate notes | Netherlands
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	100.00%		100.00%
Ratings, AAA/AA- | Securities available-for-sale | European floating rate notes | Ireland
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)			0.00%
Ratings, AAA/AA- | Securities available-for-sale | European floating rate notes | Other
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	100.00%		99.00%
Ratings, A+/A- | Non-agency RMBS
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	8.00%		9.00%
Ratings, A+/A- | Non-agency RMBS | 2005
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	21.00%		21.00%
Ratings, A+/A- | Non-agency RMBS | 2004 and earlier
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	5.00%		5.00%
Ratings, A+/A- | Commercial MBS | Domestic
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	16.00%		15.00%
Ratings, A+/A- | Commercial MBS | 2009-2015 | Domestic
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	16.00%		17.00%
Ratings, A+/A- | Commercial MBS | 2008 | Domestic
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)			0.00%
Ratings, A+/A- | Commercial MBS | 2007 | Domestic
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	21.00%		21.00%
Ratings, A+/A- | Commercial MBS | 2006 | Domestic
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	18.00%		17.00%
Ratings, A+/A- | Commercial MBS | 2004 and earlier | Domestic
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)			0.00%
Ratings, A+/A- | Sovereign debt/sovereign guaranteed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	1.00%
Ratings, A+/A- | Sovereign debt/sovereign guaranteed | Ireland
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	17.00%
Ratings, A+/A- | Alt-A RMBS
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	1.00%	[2]	1.00%	[2]
Ratings, A+/A- | Alt-A RMBS | 2005
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	3.00%	[2]	3.00%	[2]
Ratings, A+/A- | Alt-A RMBS | 2004 and earlier
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	4.00%	[2]	4.00%	[2]
Ratings, A+/A- | Securities available-for-sale | European floating rate notes
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	12.00%		12.00%
Ratings, A+/A- | Securities available-for-sale | European floating rate notes | United Kingdom
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	17.00%		17.00%
Ratings, A+/A- | Securities available-for-sale | European floating rate notes | Other
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	0.00%		1.00%
Ratings, BBB+/BBB- | Non-agency RMBS
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	19.00%		19.00%
Ratings, BBB+/BBB- | Non-agency RMBS | 2007
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)			0.00%
Ratings, BBB+/BBB- | Non-agency RMBS | 2005
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	18.00%		19.00%
Ratings, BBB+/BBB- | Non-agency RMBS | 2004 and earlier
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	27.00%		27.00%
Ratings, BBB+/BBB- | Commercial MBS | Domestic
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	3.00%		3.00%
Ratings, BBB+/BBB- | Commercial MBS | 2007 | Domestic
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	14.00%		14.00%
Ratings, BBB+/BBB- | Sovereign debt/sovereign guaranteed
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	25.00%		24.00%
Ratings, BBB+/BBB- | Sovereign debt/sovereign guaranteed | Ireland
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	83.00%		100.00%
Ratings, BBB+/BBB- | Sovereign debt/sovereign guaranteed | Spain
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	100.00%		100.00%
Ratings, BBB+/BBB- | Sovereign debt/sovereign guaranteed | Italy
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	100.00%		100.00%
Ratings, BBB+/BBB- | Sovereign debt/sovereign guaranteed | Other
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	17.00%		19.00%
Ratings, BBB+/BBB- | Alt-A RMBS
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	1.00%	[2]	1.00%	[2]
Ratings, BBB+/BBB- | Alt-A RMBS | 2006
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	1.00%	[2]	1.00%	[2]
Ratings, BBB+/BBB- | Alt-A RMBS | 2005
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	1.00%	[2]	1.00%	[2]
Ratings, BBB+/BBB- | Alt-A RMBS | 2004 and earlier
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	7.00%	[2]	7.00%	[2]
Ratings, BB+ and lower | Non-agency RMBS
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	72.00%		71.00%
Ratings, BB+ and lower | Non-agency RMBS | 2007
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	100.00%		100.00%
Ratings, BB+ and lower | Non-agency RMBS | 2006
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	100.00%		100.00%
Ratings, BB+ and lower | Non-agency RMBS | 2005
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	61.00%		60.00%
Ratings, BB+ and lower | Non-agency RMBS | 2004 and earlier
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	65.00%		65.00%
Ratings, BB+ and lower | Alt-A RMBS
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	98.00%	[2]	98.00%	[2]
Ratings, BB+ and lower | Alt-A RMBS | 2007
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	100.00%	[2]	100.00%	[2]
Ratings, BB+ and lower | Alt-A RMBS | 2006
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	99.00%	[2]	99.00%	[2]
Ratings, BB+ and lower | Alt-A RMBS | 2005
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	96.00%	[2]	96.00%	[2]
Ratings, BB+ and lower | Alt-A RMBS | 2004 and earlier
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	89.00%	[2]	89.00%	[2]
Ratings, BB+ and lower | Securities available-for-sale | European floating rate notes
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	9.00%		9.00%
Ratings, BB+ and lower | Securities available-for-sale | European floating rate notes | Ireland
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)	100.00%		100.00%
Ratings, BB+ and lower | Securities available-for-sale | European floating rate notes | Other
Fair Value, Assets and Liabilities Measured on Recurring Basis [Line Items]
Percentage Of Fair Value (percent)			0.00%

[1] At March 31, 2015 and Dec. 31, 2014, foreign covered bonds and sovereign debt were included in Level 1 and Level 2 in the valuation hierarchy. All other assets in the table are Level 2 assets in the valuation hierarchy.

[2] Previously included in the Grantor Trust. The Grantor Trust was dissolved in 2011.