Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Nonrecurring Basis (Details) - Nonrecurring - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
ASSETS MEASURED ON A NONRECURRING BASIS
Collateral-dependent loans	$ 5	$ 108
Accrued income and other assets	74	56
Total assets at fair value	79	164
Level 1
ASSETS MEASURED ON A NONRECURRING BASIS
Collateral-dependent loans	0	0
Accrued income and other assets	0	0
Total assets at fair value	0	0
Level 2
ASSETS MEASURED ON A NONRECURRING BASIS
Collateral-dependent loans	0	0
Accrued income and other assets	0	0
Total assets at fair value	0	0
Level 3
ASSETS MEASURED ON A NONRECURRING BASIS
Collateral-dependent loans	5	108
Accrued income and other assets	74	56
Total assets at fair value	$ 79	$ 164