SHAREHOLDERS' EQUITY - Reclassifications Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		1 Months Ended	3 Months Ended								12 Months Ended
		Jan. 31, 2018	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other-than-temporary impairment losses realized											$ (81)
Other-than-temporary impairment losses realized													$ (37)		$ (85)
Other gains (losses)	[1]										(349)		(114)		71
Total before tax			$ 722	$ 1,146	$ 1,131	$ 982	$ 999	$ 1,075	$ 1,045	$ 898	3,983		4,018		4,067
Income tax (expense) benefit			$ (197)	$ (301)	$ (299)	$ (265)	$ 1,585	$ (359)	$ (332)	$ (306)	(1,063)		586		(1,408)
Net of tax											$ 2,920		$ 4,604		$ 2,659
Blended statutory income tax rate											27.00%
U.S. federal statutory corporate income tax rate		21.00%									21.00%		35.00%		35.00%
Reclassification out of Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net of tax											$ (47)		$ (12)		$ 32
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											(63)
Other-than-temporary impairment losses realized													(29)		(83)
Other gains (losses)											17		27		136
Total before tax											(46)		(2)		53
Income tax (expense) benefit											12	[2]	1	[3]	(18)	[3]
Net of tax											(34)		(1)		35
Reclassification out of Accumulated Other Comprehensive Income | Pension liability adjustment
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Acquisition and operating expense, actuarial gains (losses)	[4]										(18)		(17)		(15)
Acquisition and operating expenses, prior service (cost) credit	[4]										0		0		11
Income tax (expense) benefit											5	[2]	6	[3]	1	[3]
Net of tax											$ (13)		$ (11)		$ (3)

[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 27% blended tax rate

[3] Based on 35% tax rate

[4] These accumulated other comprehensive income components are included in the computation of net periodic pension cost (see Note 14 for additional details).