Regulatory Requirements - U.S. Bank Subsidiaries' Regulatory Capital and Capital Ratios (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Required Ratio
Common Equity Tier 1 capital (as a percent)	10.00%	8.60%
Tier 1 capital (as a percent)	11.50%	10.10%
Total capital (as a percent)	13.50%	12.10%
Tier 1 leverage (as a percent)	4.00%	4.00%
SLR (as a percent)	5.00%	5.00%
Amount
Common Equity Tier 1 capital	$ 64,348	$ 62,086
Tier 1 capital	72,937	70,619
Total capital	82,661	80,052
Tier 1 leverage	72,937	70,619
SLR	$ 72,937	$ 70,619
Ratio
Common Equity Tier 1 capital (as a percent)	16.30%	16.90%
Tier 1 capital (as a percent)	18.50%	19.20%
Total capital (as a percent)	20.90%	21.80%
Tier 1 leverage (as a percent)	8.20%	8.40%
SLR (as a percent)	6.30%	6.50%
MSBNA
Required Ratio
Common Equity Tier 1 capital (as a percent)	6.50%	6.50%
Tier 1 capital (as a percent)	8.00%	8.00%
Total capital (as a percent)	10.00%	10.00%
Tier 1 leverage (as a percent)	5.00%	5.00%
SLR (as a percent)	6.00%	6.00%
Amount
Common Equity Tier 1 capital	$ 16,641	$ 15,221
Tier 1 capital	16,641	15,221
Total capital	16,953	15,484
Tier 1 leverage	16,641	15,221
SLR	$ 16,641	$ 15,221
Ratio
Common Equity Tier 1 capital (as a percent)	19.90%	19.50%
Tier 1 capital (as a percent)	19.90%	19.50%
Total capital (as a percent)	20.30%	19.80%
Tier 1 leverage (as a percent)	11.90%	10.50%
SLR (as a percent)	9.20%	8.20%
MSPBNA
Required Ratio
Common Equity Tier 1 capital (as a percent)	6.50%	6.50%
Tier 1 capital (as a percent)	8.00%	8.00%
Total capital (as a percent)	10.00%	10.00%
Tier 1 leverage (as a percent)	5.00%	5.00%
SLR (as a percent)	6.00%	6.00%
Amount
Common Equity Tier 1 capital	$ 8,281	$ 7,183
Tier 1 capital	8,281	7,183
Total capital	8,331	7,229
Tier 1 leverage	8,281	7,183
SLR	$ 8,281	$ 7,183
Ratio
Common Equity Tier 1 capital (as a percent)	27.30%	25.20%
Tier 1 capital (as a percent)	27.30%	25.20%
Total capital (as a percent)	27.50%	25.40%
Tier 1 leverage (as a percent)	10.80%	10.00%
SLR (as a percent)	10.30%	9.60%