Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Nonrecurring Basis (Details) - Nonrecurring [Member] - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019
ASSETS MEASURED ON A NONRECURRING BASIS
Impaired loans and leases	$ 33		$ 76
Accrued income and other assets	64		169
Total assets at fair value	97		$ 245
Level 1 [Member]
ASSETS MEASURED ON A NONRECURRING BASIS
Impaired loans and leases	0	$ 0
Accrued income and other assets	0	0
Total assets at fair value	0	0
Level 2 [Member]
ASSETS MEASURED ON A NONRECURRING BASIS
Impaired loans and leases	0	0
Accrued income and other assets	0	118
Total assets at fair value	0	118
Level 3 [Member]
ASSETS MEASURED ON A NONRECURRING BASIS
Impaired loans and leases	33	76
Accrued income and other assets	64	51
Total assets at fair value	$ 97	$ 127