Regulatory Requirements (Significant U.S. Bank Operating Subsidiaries' Capital) (Details) - U.S. Basel III - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Transitional / Advanced Approach
Regulatory Requirements
Common Equity Tier 1 capital, amount	$ 59,056	$ 57,324
Tier 1 capital, amount	66,071	64,182
Total capital, amount	$ 78,921	$ 74,972
Ratio
Common Equity Tier 1 capital ratio	14.00%	12.60%
Tier 1 capital ratio	15.60%	14.10%
Total capital ratio	18.60%	16.40%
Tier 1 leverage ratio	8.10%	7.90%
MSBNA
Required Capital Ratio
Common Equity Tier 1 capital ratio, required	6.50%	6.50%
Tier 1 capital ratio, required	8.00%	8.00%
Total capital ratio, required	10.00%	10.00%
Teir 1 leverage ratio, required	5.00%	5.00%
MSBNA | Transitional / Standardized Approach
Regulatory Requirements
Common Equity Tier 1 capital, amount	$ 12,939
Tier 1 capital, amount	12,939
Total capital, amount	14,649
Tier 1 leverage capital, amount	$ 12,939
Ratio
Common Equity Tier 1 capital ratio	13.80%
Tier 1 capital ratio	13.80%
Total capital ratio	15.70%
Tier 1 leverage ratio	10.10%
MSBNA | Transitional / U.S. Basel I And Basel 2.5 Approach
Regulatory Requirements
Common Equity Tier 1 capital, amount		$ 12,355
Tier 1 capital, amount		12,355
Total capital, amount		14,040
Tier 1 leverage capital, amount		$ 12,355
Ratio
Common Equity Tier 1 capital ratio		12.20%
Tier 1 capital ratio		12.20%
Total capital ratio		13.90%
Tier 1 leverage ratio		10.20%
MSPBNA
Required Capital Ratio
Common Equity Tier 1 capital ratio, required	6.50%	6.50%
Tier 1 capital ratio, required	8.00%	8.00%
Total capital ratio, required	10.00%	10.00%
Teir 1 leverage ratio, required	5.00%	5.00%
MSPBNA | Transitional / Standardized Approach
Regulatory Requirements
Common Equity Tier 1 capital, amount	$ 3,433
Tier 1 capital, amount	3,433
Total capital, amount	3,447
Tier 1 leverage capital, amount	$ 3,433
Ratio
Common Equity Tier 1 capital ratio	23.00%
Tier 1 capital ratio	23.00%
Total capital ratio	23.10%
Tier 1 leverage ratio	9.90%
MSPBNA | Transitional / U.S. Basel I And Basel 2.5 Approach
Regulatory Requirements
Common Equity Tier 1 capital, amount		$ 2,468
Tier 1 capital, amount		2,468
Total capital, amount		2,480
Tier 1 leverage capital, amount		$ 2,468
Ratio
Common Equity Tier 1 capital ratio		20.30%
Tier 1 capital ratio		20.30%
Total capital ratio		20.40%
Tier 1 leverage ratio		9.40%