INVESTMENTS - Net Effect on Shareholders' Equity of Unrealized Gains and Losses from Investment Securities (Detail) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Mar. 31, 2018	Dec. 31, 2017
Investments [Abstract]
Unrealized Gains (Losses) on Available-for-sale Securities	[1]	$ 7,426	$ 9,358
Deferred income taxes	[1]	(2,220)	(3,394)
Shareholders' equity, unrealized gains (losses) on investment securities	[1],[2]	$ 5,206	$ 5,964

[1] See Note 1 for discussion of the accounting treatment of tax on amounts recorded in accumulated other comprehensive income pursuant to the Tax Act and for the adoption of accounting guidance on January 1, 2018 related to financial instruments.

[2] See Note 1 of the Notes to the Consolidated Financial Statements for the adoption of accounting guidance on January 1, 2018 related to financial instruments.