SHAREHOLDERS' EQUITY - Reclassifications Out of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended								9 Months Ended
		Sep. 30, 2019		Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018		Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019		Sep. 30, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other gains (losses)		$ (135)				$ 61				$ (126)		$ (59)
Total before tax		1,036				1,146				3,388		3,261
Income tax (expense) or benefit		(259)				(301)				(865)		(866)
Net of tax		$ 777		$ 817	$ 928	$ 845		$ 832	$ 717	$ 2,523		$ 2,395
Blended statutory income tax rate		25.00%				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		$ (35)				$ 24				$ (8)		$ 0
Reclassification Out Of Accumulated Other Comprehensive Income | Unrealized gains (losses) on available-for-sale securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other-than-temporary impairment losses realized		(14)				0				(13)		(2)
Other gains (losses)		(27)				37				14		13
Total before tax		(41)				37				1		11
Income tax (expense) or benefit		10	[1]			(10)	[2]			0	[2]	(3)	[3]
Net of tax		(31)				27				1		8
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)	[4]	(5)				(5)				(12)		(13)
Acquisition and operating expenses, prior service (cost) credit	[4]	0				0				0		0
Income tax (expense) or benefit		1	[1]			2	[2]			3	[2]	5	[3]
Net of tax		$ (4)				$ (3)				$ (9)		$ (8)

[1] Based on 25% blended tax rate

[2] Based on 26% blended tax rate

[3] Based on 27% blended tax rate

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