FAIR VALUE MEASUREMENT - Items Measured at Fair Value on a Nonrecurring Basis (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Items Measured at Fair Value on a Nonrecurring Basis
Non-marketable equity securities measured using the measurement alternative	$ 7,523	$ 7,212
Nonrecurring | Level 2
Items Measured at Fair Value on a Nonrecurring Basis
Loans held-for-sale	3,249	3,261
Other real estate owned	6	62
Loans	93	139
Non-marketable equity securities measured using the measurement alternative	249	192
Total assets	3,597	3,654
Nonrecurring | Level 3
Items Measured at Fair Value on a Nonrecurring Basis
Loans held-for-sale	1,330	1,794
Other real estate owned	14	16
Loans	251	251
Non-marketable equity securities measured using the measurement alternative	0	69
Total assets	1,595	2,130
Fair value | Nonrecurring
Items Measured at Fair Value on a Nonrecurring Basis
Loans held-for-sale	4,579	5,055
Other real estate owned	20	78
Loans	344	390
Non-marketable equity securities measured using the measurement alternative	249	261
Total assets	$ 5,192	$ 5,784