ACCUMULATED OTHER COMPREHENSIVE INCOME (LOSS) - Changes in AOCI by Component (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	$ 13,154	$ 12,061	$ 13,625	$ 11,274	$ 11,274
Other comprehensive income (loss) on investments in net expected credit losses	(1)	28	(1)	26
Ending balance	12,933	12,731	12,933	12,731	13,625	$ 11,274
Total Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	2,813	2,225	3,548	1,413	1,413
Other comprehensive income (loss) before reclassifications	(265)	483	(966)	1,263
Other comprehensive income (loss) on investments in net expected credit losses	(1)	28	(1)	26
Amounts reclassified from accumulated other comprehensive income (loss)	(4)	28	(38)	62
Ending balance	2,543	2,764	2,543	2,764	3,548	1,413
Unrealized Gains and Losses on Investments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	2,818	2,233	3,556	1,421	1,421
Other comprehensive income (loss) before reclassifications	(263)	482	(967)	1,264
Other comprehensive income (loss) on investments in net expected credit losses	(1)	28	(1)	26
Amounts reclassified from accumulated other comprehensive income (loss)	(5)	28	(39)	60
Ending balance	2,549	2,771	2,549	2,771	3,556	1,421
Offset of net unrealized gains in AOCI due to impact those net unrealized losses would have on certain of the Company's insurance assets and liabilities had the net unrealized losses been recognized in net income			(1,700)	(1,600)	(2,000)	(777)
Accumulated Gain and Loss Derivatives
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Beginning balance	(5)	(8)	(8)	(8)	(8)
Other comprehensive income (loss) before reclassifications	(2)	1	1	(1)
Other comprehensive income (loss) on investments in net expected credit losses	0	0		0
Amounts reclassified from accumulated other comprehensive income (loss)	1	0	1	2
Ending balance	$ (6)	$ (7)	$ (6)	$ (7)	$ (8)	$ (8)