INVESTMENTS - Available-for-sale Securities (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 44,926	$ 42,492
Gross Unrealized Gains	1,438	618
Gross Unrealized Losses	435	1,195
Fair Value	45,929	41,915
OTTI in AOCI	2	2
Amortized Cost
Subtotal	43,711
Fair Value
Subtotal	44,694
March 31, 2019	45,929
Corporate
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	30,106	26,690
Gross Unrealized Gains	867	385
Gross Unrealized Losses	208	699
Fair Value	30,765	26,376
OTTI in AOCI	0	0
U.S. Treasury, government and agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	12,719	13,646
Gross Unrealized Gains	462	143
Gross Unrealized Losses	213	454
Fair Value	12,968	13,335
OTTI in AOCI	0	0
State and Political Sub-divisions
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	408	408
Gross Unrealized Gains	55	47
Gross Unrealized Losses	0	1
Fair Value	463	454
OTTI in AOCI	0	0
Foreign governments
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	478	515
Gross Unrealized Gains	27	17
Gross Unrealized Losses	7	13
Fair Value	498	519
OTTI in AOCI	0	0
Residential mortgage-backed
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	185	193
Gross Unrealized Gains	10	9
Gross Unrealized Losses	0	0
Fair Value	195	202
OTTI in AOCI	0	0
Amortized Cost
Without single maturity date	185
Fair Value
Without single maturity date	195
Asset- backed
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	608	600
Gross Unrealized Gains	1	1
Gross Unrealized Losses	4	11
Fair Value	605	590
OTTI in AOCI	2	2
Amortized Cost
Without single maturity date	608
Fair Value
Without single maturity date	605
Redeemable preferred stock
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	422	440
Gross Unrealized Gains	16	16
Gross Unrealized Losses	3	17
Fair Value	435	439
OTTI in AOCI	0	$ 0
Amortized Cost
Without single maturity date	422
Fair Value
Without single maturity date	435
Total Fixed Maturities
Amortized Cost
Due in one year or less	1,817
Due in years two through five	10,322
Due in years six through ten	14,953
Due after ten years	16,619
Fair Value
Due in one year or less	1,829
Due in years two through five	10,519
Due in years six through ten	15,367
Due after ten years	$ 16,979