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Regulatory and Capital Adequacy - Capital Ratios Under Basel III (Details) $ in Millions | Dec. 31, 2020 USD ($) | Dec. 31, 2019 USD ($)
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Common equity Tier 1 capital: |  |
Common equity Tier 1 capital | $ 40,736 | $ 38,162
Common equity Tier 1 capital, capital ratio | 0.137 | 0.122
Common equity Tier 1 capital, minimum capital adequacy | 0.045 | 0.045
Tier 1 risk-based capital: |  |
Tier 1 capital | $ 45,583 | $ 43,015
Tier 1 capital, capital ratio | 0.153 | 0.137
Tier 1 capital, minimum capital adequacy | 0.060 | 0.060
Tier 1 capital, well-capitalized | 0.060 | 0.060
Total risk-based capital: |  |
Total capital | $ 52,788 | $ 50,348
Total capital, capital ratio | 0.177 | 0.161
Total capital, minimum capital adequacy | 0.080 | 0.080
Total capital, well-capitalized | 0.100 | 0.100
Tier 1 leverage capital: |  |
Tier 1 leverage capital | $ 45,583 | $ 43,015
Tier 1 leverage, capital ratio | 0.112 | 0.117
Tier 1 leverage, minimum capital adequacy | 0.040 | 0.040
Supplementary leverage: |  |
Tier one capital under BaselIII standardized approach | $ 45,583 | $ 43,015
Basel III Supplementary Leverage Ratio | 0.107 | 0.099
Supplementary leverage | 0.030 | 0.030
Capital One Bank (USA), N.A. |  |
Common equity Tier 1 capital: |  |
Common equity Tier 1 capital | $ 19,924 | $ 17,883
Common equity Tier 1 capital, capital ratio | 0.215 | 0.161
Common equity Tier 1 capital, minimum capital adequacy | 0.045 | 0.045
Common equity Tie 1 capital, well capitalized | 0.065 | 0.065
Tier 1 risk-based capital: |  |
Tier 1 capital | $ 19,924 | $ 17,883
Tier 1 capital, capital ratio | 0.215 | 0.161
Tier 1 capital, minimum capital adequacy | 0.060 | 0.060
Tier 1 capital, well-capitalized | 0.080 | 0.080
Total risk-based capital: |  |
Total capital | $ 21,708 | $ 20,109
Total capital, capital ratio | 0.234 | 0.181
Total capital, minimum capital adequacy | 0.080 | 0.080
Total capital, well-capitalized | 0.100 | 0.100
Tier 1 leverage capital: |  |
Tier 1 leverage capital | $ 19,924 | $ 17,883
Tier 1 leverage, capital ratio | 0.183 | 0.148
Tier 1 leverage, minimum capital adequacy | 0.040 | 0.040
Tier 1 leverage, well-capitalized | 0.050 | 0.050
Supplementary leverage: |  |
Tier one capital under BaselIII standardized approach | $ 19,924 | $ 17,883
Basel III Supplementary Leverage Ratio | 0.147 | 0.121
Supplementary leverage | 0.030 | 0.030
Capital One, N.A. |  |
Common equity Tier 1 capital: |  |
Common equity Tier 1 capital | $ 26,671 | $ 28,445
Common equity Tier 1 capital, capital ratio | 0.124 | 0.134
Common equity Tier 1 capital, minimum capital adequacy | 0.045 | 0.045
Common equity Tie 1 capital, well capitalized | 0.065 | 0.065
Tier 1 risk-based capital: |  |
Tier 1 capital | $ 26,671 | $ 28,445
Tier 1 capital, capital ratio | 0.124 | 0.134
Tier 1 capital, minimum capital adequacy | 0.060 | 0.060
Tier 1 capital, well-capitalized | 0.080 | 0.080
Total risk-based capital: |  |
Total capital | $ 29,369 | $ 30,852
Total capital, capital ratio | 0.137 | 0.145
Total capital, minimum capital adequacy | 0.080 | 0.080
Total capital, well-capitalized | 0.100 | 0.100
Tier 1 leverage capital: |  |
Tier 1 leverage capital | $ 26,671 | $ 28,445
Tier 1 leverage, capital ratio | 0.076 | 0.092
Tier 1 leverage, minimum capital adequacy | 0.040 | 0.040
Tier 1 leverage, well-capitalized | 0.050 | 0.050
Supplementary leverage: |  |
Tier one capital under BaselIII standardized approach | $ 26,671 | $ 28,445
Basel III Supplementary Leverage Ratio | 0.069 | 0.082
Supplementary leverage | 0.030 | 0.030

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