Schedule of Credit Default Swaps where we Sell Protection on Credit Default Swap Index Tranches and Fair Values (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014		Dec. 31, 2013
Derivative [Line Items]
Notional value	$ 22,843		$ 23,263
Index Tranches | Original Index Tranche Attachment/Detachment Point And Maturity | Credit default swaps
Derivative [Line Items]
Notional value	600		600
Index Tranches | Securitization Entities | Credit default swaps
Derivative [Line Items]
Notional value	312		312
Index Tranches | Securitization Entities | Portion Backing Third-Party Borrowings Maturing 2017 | Credit default swaps
Derivative [Line Items]
Notional value	12	[1]	12	[1]
Index Tranches | Securitization Entities | Portion Backing Interest Maturing 2017 | Credit default swaps
Derivative [Line Items]
Notional value	300	[2]	300	[2]
7% - 15% | Index Tranches | Original Index Tranche Attachment/Detachment Point And Maturity | Matures After One Year Through Five Years | Credit default swaps
Derivative [Line Items]
Current attachment percentage	7.00%		7.00%
Current detachment percentage	15.00%		15.00%
Notional value	100	[3]	100	[3]
9% - 12% | Index Tranches | Original Index Tranche Attachment/Detachment Point And Maturity | Matures Less Than One Year | Credit default swaps
Derivative [Line Items]
Current attachment percentage	9.00%		9.00%
Current detachment percentage	12.00%		12.00%
Notional value	250	[4]	0	[4]
9% - 12% | Index Tranches | Original Index Tranche Attachment/Detachment Point And Maturity | Matures After One Year Through Five Years | Credit default swaps
Derivative [Line Items]
Current attachment percentage	9.00%		9.00%
Current detachment percentage	12.00%		12.00%
Notional value	0	[4]	250	[4]
10% - 15% | Index Tranches | Original Index Tranche Attachment/Detachment Point And Maturity | Matures Less Than One Year | Credit default swaps
Derivative [Line Items]
Current attachment percentage	10.00%		10.00%
Current detachment percentage	15.00%		15.00%
Notional value	250	[5]	250	[5]
Original Amount | Securitization Entities | Portion Backing Third-Party Borrowings Maturing 2017
Derivative [Line Items]
Notional value	39
Original Amount | Securitization Entities | Portion Backing Interest Maturing 2017
Derivative [Line Items]
Notional value	$ 300

[1] Original notional value was $39 million.

[2] Original notional value was $300 million.

[3] The current attachment/detachment as of September 30, 2014 and December 31, 2013 was 7% - 15%.

[4] The current attachment/detachment as of September 30, 2014 and December 31, 2013 was 9% - 12%.

[5] The current attachment/detachment as of September 30, 2014 and December 31, 2013 was 10% - 15%.