Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Nonrecurring Basis (Details) - Nonrecurring - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
ASSETS MEASURED ON A NONRECURRING BASIS
Collateral-dependent loans	$ 89	$ 76
Accrued income and other assets	103	169
Total assets at fair value	192	245
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	118
Total assets at fair value	0	118
Level 3
ASSETS MEASURED ON A NONRECURRING BASIS
Collateral-dependent loans	89	76
Accrued income and other assets	103	51
Total assets at fair value	$ 192	$ 127