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	Jun. 30, 2014	Dec. 31, 2013
Down Scenario [Member] | MSR Portfolio [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	$ (508)	$ (435)
Net fair value 50 basis points	(232)	(199)
Net fair value 25 basis points	(110)	(93)
Down Scenario [Member] | Derivative instrument hedges [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	409	399
Net fair value 50 basis points	209	194
Net fair value 25 basis points	103	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	(23)	(5)
Net fair value 25 basis points	(7)	(2)
Up Scenario [Member] | MSR Portfolio [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	324	287
Net fair value 50 basis points	175	154
Net fair value 25 basis points	94	82
Up Scenario [Member] | Derivative instrument hedges [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	(335)	(301)
Net fair value 50 basis points	(181)	(157)
Net fair value 25 basis points	(96)	(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	(11)	(14)
Net fair value 50 basis points	(6)	(3)
Net fair value 25 basis points	$ (2)