Securitizations and Variable Interest Entities, Key Economic Assumptions - Mortgage Servicing Rights (Details) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2015 USD ($) $ / loan	Dec. 31, 2014 USD ($) $ / loan
Decrease in fair value from:
200 basis point increase	$ 55	$ 130
Residential 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]
Fair value of interests held	$ 12,661	$ 12,738
Expected weighted-average life (in years)	5 years 10 months 24 days	5 years 8 months 12 days
Key economic assumptions:
Prepayment speed assumption	11.60%	12.50%
Decrease in fair value from:
10% adverse change	$ 701	$ 738
25% adverse change	$ 1,668	$ 1,754
Discount rate assumption	7.40%	7.60%
Decrease in fair value from:
100 basis point increase	$ 629	$ 617
200 basis point increase	$ 1,200	$ 1,178
Cost to service assumption ($ per loan) | $ / loan	169	179
Decrease in fair value from:
10% adverse change | $ / loan	586	579
25% adverse change | $ / loan	1,465	1,433
Interest-Only Strips [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]
Fair value of interests held	$ 102	$ 117
Expected weighted-average life (in years)	1 year 4 months 24 days	3 years 10 months 24 days
Key economic assumptions:
Prepayment speed assumption	10.50%	11.40%
Decrease in fair value from:
10% adverse change	$ 1	$ 2
25% adverse change	$ 3	$ 6
Discount rate assumption	10.60%	18.70%
Decrease in fair value from:
100 basis point increase	$ 1	$ 2
200 basis point increase	2	4
Subordinated bonds [Member] | Commercial Securitizations [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]
Fair value of interests held	$ 363	$ 294
Expected weighted-average life (in years)	2 years 2 months 12 days	2 years 10 months 24 days
Decrease in fair value from:
Discount rate assumption	4.30%	4.70%
Decrease in fair value from:
100 basis point increase	$ 7	$ 8
200 basis point increase	$ 14	$ 15
Decrease in fair value from:
Credit loss assumption	3.00%	4.10%
Decrease in fair value from:
10% higher losses	$ 1	$ 3
25% higher losses	7	10
Subordinated bonds [Member] | Consumer Securitizations [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]
Fair value of interests held	$ 34	$ 36
Expected weighted-average life (in years)	5 years 2 months 12 days	5 years 6 months
Key economic assumptions:
Prepayment speed assumption	8.10%	7.10%
Decrease in fair value from:
10% adverse change	$ 0	$ 0
25% adverse change	$ 0	$ 0
Discount rate assumption	4.20%	3.90%
Decrease in fair value from:
100 basis point increase	$ 1	$ 2
200 basis point increase	$ 3	$ 3
Decrease in fair value from:
Credit loss assumption	0.30%	0.40%
Decrease in fair value from:
10% higher losses	$ 0	$ 0
25% higher losses	0	0
Senior bonds [Member] | Commercial Securitizations [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]
Fair value of interests held	$ 590	$ 546
Expected weighted-average life (in years)	5 years 4 months 24 days	6 years 2 months 12 days
Decrease in fair value from:
Discount rate assumption	2.60%	2.80%
Decrease in fair value from:
100 basis point increase	$ 27	$ 29
200 basis point increase	$ 53	$ 55
Decrease in fair value from:
Credit loss assumption	0.00%	0.00%
Decrease in fair value from:
10% higher losses	$ 0	$ 0
25% higher losses	$ 0	$ 0