Fair Values (Details 2) - USD ($) $ in Billions	Sep. 30, 2021	Dec. 31, 2020
Carrying Value
Financial assets for which carrying values equal or approximate fair value
Cash and cash equivalents	$ 0.7	$ 0.6
Other financial assets	13.6	12.1
Financial assets carried at other than fair value
Loans to affiliates and other	9.2	10.9
Financial Liabilities:
Financial liabilities for which carrying values equal or approximate fair value	13.6	12.6
Financial liabilities carried at other than fair value
Long-term debt	5.2	7.0
Long-term debt to affiliates	1.3	0.8
Carrying Value | Card Member Loans
Financial assets carried at other than fair value
Card Member loans, less reserves for credit losses	0.5	0.5
Corresponding Fair Value Amount
Financial assets for which carrying values equal or approximate fair value
Cash and cash equivalents	0.7	0.6
Other financial assets	13.6	12.1
Financial assets carried at other than fair value
Loans to affiliates and other	9.2	11.1
Financial Liabilities:
Financial liabilities for which carrying values equal or approximate fair value	13.6	12.6
Financial liabilities carried at other than fair value
Long-term debt	5.5	7.4
Long-term debt to affiliates	1.3	0.8
Corresponding Fair Value Amount | Card Member Loans
Financial assets carried at other than fair value
Card Member loans, less reserves for credit losses	0.5	0.5
Corresponding Fair Value Amount | Level 1
Financial assets for which carrying values equal or approximate fair value
Cash and cash equivalents	0.4	0.6
Other financial assets	0.0	0.0
Financial assets carried at other than fair value
Loans to affiliates and other	0.0	0.0
Financial Liabilities:
Financial liabilities for which carrying values equal or approximate fair value	0.0	0.0
Financial liabilities carried at other than fair value
Long-term debt	0.0	0.0
Long-term debt to affiliates	0.0	0.0
Corresponding Fair Value Amount | Level 1 | Card Member Loans
Financial assets carried at other than fair value
Card Member loans, less reserves for credit losses	0.0	0.0
Corresponding Fair Value Amount | Level 2
Financial assets for which carrying values equal or approximate fair value
Cash and cash equivalents	0.3	0.0
Other financial assets	13.6	12.1
Financial assets carried at other than fair value
Loans to affiliates and other	2.8	5.0
Financial Liabilities:
Financial liabilities for which carrying values equal or approximate fair value	13.6	12.6
Financial liabilities carried at other than fair value
Long-term debt	5.5	7.4
Long-term debt to affiliates	1.3	0.8
Corresponding Fair Value Amount | Level 2 | Card Member Loans
Financial assets carried at other than fair value
Card Member loans, less reserves for credit losses	0.0	0.0
Corresponding Fair Value Amount | Level 3
Financial assets for which carrying values equal or approximate fair value
Cash and cash equivalents	0.0	0.0
Other financial assets	0.0	0.0
Financial assets carried at other than fair value
Loans to affiliates and other	6.4	6.1
Financial Liabilities:
Financial liabilities for which carrying values equal or approximate fair value	0.0	0.0
Financial liabilities carried at other than fair value
Long-term debt	0.0	0.0
Long-term debt to affiliates	0.0	0.0
Corresponding Fair Value Amount | Level 3 | Card Member Loans
Financial assets carried at other than fair value
Card Member loans, less reserves for credit losses	$ 0.5	$ 0.5