Mortgage Servicing Rights - Sensitivity to Changes in Interest Rates to Fair Value of MSRs Portfolio and Related Derivative Instruments (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Down Scenario [Member] | Mortgage Servicing Rights [Member]
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Net fair value 100 basis points	$ (490)	$ (435)
Net fair value 50 basis points	(212)	(199)
Net fair value 25 basis points	(99)	(93)
Down Scenario [Member] | Derivative [Member]
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Net fair value 100 basis points	391	399
Net fair value 50 basis points	196	194
Net fair value 25 basis points	94	91
Down Scenario [Member] | Net sensitivity [Member]
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Net fair value 100 basis points	(99)	(36)
Net fair value 50 basis points	(16)	(5)
Net fair value 25 basis points	(5)	(2)
Up Scenario [Member] | Mortgage Servicing Rights [Member]
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Net fair value 100 basis points	297	287
Net fair value 50 basis points	157	154
Net fair value 25 basis points	84	82
Up Scenario [Member] | Derivative [Member]
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Net fair value 100 basis points	(319)	(301)
Net fair value 50 basis points	(167)	(157)
Net fair value 25 basis points	(87)	(82)
Up Scenario [Member] | Net sensitivity [Member]
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Net fair value 100 basis points	(22)	(14)
Net fair value 50 basis points	(10)	(3)
Net fair value 25 basis points	$ (3)