SHAREHOLDERS' EQUITY - Reclassifications Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended						6 Months Ended
		Jun. 30, 2019		Mar. 31, 2019	Jun. 30, 2018		Mar. 31, 2018	Jun. 30, 2019		Jun. 30, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other gains (losses)		$ (64)			$ 8			$ 9		$ (119)
Total before tax		1,109			1,131			2,351		2,114
Income tax (expense) or benefit		(292)			(299)			(606)		(564)
Net of tax		$ 817		$ 928	$ 832		$ 717	$ 1,745		$ 1,550
Blended statutory income tax rate		26.00%			26.00%			26.00%		27.00%
Reclassification Out Of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net of tax		$ 16			$ (24)			$ 27		$ (24)
Reclassification Out Of Accumulated Other Comprehensive Income | Unrealized gains (losses) on investment securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other-than-temporary impairment losses realized		0			(2)			0		(2)
Other gains (losses)		25			(26)			43		(24)
Total before tax		25			(28)			43		(26)
Income tax (expense) or benefit		(7)	[1]		7	[1]		(11)	[1]	7	[2]
Net of tax		18			(21)			32		(19)
Reclassification Out Of Accumulated Other Comprehensive Income | Pension liability adjustment
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Acquisition and operating expenses, actuarial gains (losses)	[3]	(3)			(4)			(7)		(8)
Acquisition and operating expenses, prior service (cost) credit	[3]	0			0			0		0
Income tax (expense) or benefit		1	[1]		1	[1]		2	[1]	3	[2]
Net of tax		$ (2)			$ (3)			$ (5)		$ (5)

[1] Based on 26% blended tax rate

[2] Based on 27% blended tax rate

[3] These accumulated other comprehensive income components are included in the computation of net periodic pension cost (see Note 11 for additional details).