SHAREHOLDERS' EQUITY - Reclassifications Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		1 Months Ended	3 Months Ended				6 Months Ended				12 Months Ended
		Jan. 31, 2018	Jun. 30, 2018		Jun. 30, 2017		Jun. 30, 2018		Jun. 30, 2017		Dec. 31, 2017
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other-than-temporary impairment losses realized			$ (5)				$ (12)
Other than temporary impairment losses realized					$ (9)				$ (19)
Other gains (losses)	[1]		8		(47)		(119)		(177)
Total before tax			1,131		1,045		2,114		1,944
Income tax (expense) or benefit			(299)		(332)		(564)		(639)
Net of tax			$ 832		$ 713		$ 1,550		1,305
Blended statutory income tax rate			26.00%				27.00%
U.S. federal statutory corporate income tax rate		21.00%			35.00%		21.00%				35.00%
Reclassification Out Of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net of tax			$ (24)		$ (4)		$ (24)		(16)
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			(2)				(2)
Other than temporary impairment losses realized					(6)				(16)
Other gains (losses)			(26)		5		(24)		(1)
Total before tax			(28)		(1)		(26)		(17)
Income tax (expense) or benefit			7	[2]	0	[3]	7	[4]	6	[3]
Net of tax			(21)		(1)		(19)		(11)
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)	[5]		(4)		(5)		(8)		(8)
Acquisition and operating expenses, prior service (cost) credit	[5]		0		0		0		0
Income tax (expense) or benefit			1	[2]	2	[3]	3	[4]	3	[3]
Net of tax			$ (3)		$ (3)		$ (5)		$ (5)

[1] 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.

[2] Based on 26% blended tax rate

[3] Based on 35% tax rate

[4] Based on 27% blended tax rate

[5] These accumulated other comprehensive income components are included in the computation of net periodic pension cost (see Note 12 for additional details)