BENEFITS PAYABLE - Activity in Benefits Payable (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Balances at January 1	$ 4,563,000,000	$ 4,976,000,000	$ 4,475,000,000
Less: Premium deficiency reserve	0	(176,000,000)	0
Less: Reinsurance recoverables	(76,000,000)	(85,000,000)	(78,000,000)
Balances at January 1, net		4,487,000,000	4,715,000,000	$ 4,397,000,000
Current year, Incurred	44,001,000,000	45,318,000,000	44,397,000,000
Prior years, Incurred	(483,000,000)	(582,000,000)	(236,000,000)
Total incurred	43,518,000,000	44,736,000,000	44,161,000,000
Current year, Paid	(39,496,000,000)	(40,852,000,000)	(39,802,000,000)
Prior years, Paid	(3,911,000,000)	(4,112,000,000)	(4,041,000,000)
Total paid	(43,407,000,000)	(44,964,000,000)	(43,843,000,000)
Premium deficiency reserve	0	0	176,000,000
Reinsurance recoverable	70,000,000	76,000,000	85,000,000
Balances at December 31	4,668,000,000	4,563,000,000	4,976,000,000
Retail
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Balances at January 1	3,506,000,000	3,600,000,000	3,428,000,000
Less: Reinsurance recoverables	(76,000,000)	(85,000,000)	(78,000,000)
Balances at January 1, net		3,430,000,000	3,515,000,000	3,350,000,000
Current year, Incurred	38,604,000,000	37,212,000,000	36,299,000,000
Prior years, Incurred	(386,000,000)	(429,000,000)	(248,000,000)
Total incurred	38,218,000,000	36,783,000,000	36,051,000,000
Current year, Paid	(34,781,000,000)	(33,784,000,000)	(32,874,000,000)
Prior years, Paid	(2,974,000,000)	(3,084,000,000)	(3,012,000,000)
Total paid	(37,755,000,000)	(36,868,000,000)	(35,886,000,000)
Reinsurance recoverable	70,000,000	76,000,000	85,000,000
Balances at December 31	3,963,000,000	3,506,000,000	3,600,000,000
Group and Specialty
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Balances at January 1	579,000,000	616,000,000	603,000,000
Less: Reinsurance recoverables	0	0	0
Balances at January 1, net		579,000,000	616,000,000	603,000,000
Current year, Incurred	5,403,000,000	5,271,000,000	5,377,000,000
Prior years, Incurred	(40,000,000)	(46,000,000)	(7,000,000)
Total incurred	5,363,000,000	5,225,000,000	5,370,000,000
Current year, Paid	(4,843,000,000)	(4,700,000,000)	(4,774,000,000)
Prior years, Paid	(531,000,000)	(562,000,000)	(583,000,000)
Total paid	(5,374,000,000)	(5,262,000,000)	(5,357,000,000)
Reinsurance recoverable		0	0
Balances at December 31	568,000,000	579,000,000	616,000,000
Individual Commercial
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Balances at January 1	454,000,000	741,000,000	424,000,000
Less: Premium deficiency reserve	0	(176,000,000)	0
Balances at January 1, net		454,000,000	565,000,000	$ 424,000,000
Current year, Incurred	669,000,000	3,677,000,000	3,512,000,000
Prior years, Incurred	(56,000,000)	(106,000,000)	20,000,000
Total incurred	613,000,000	3,571,000,000	3,532,000,000
Current year, Paid	(583,000,000)	(3,233,000,000)	(2,966,000,000)
Prior years, Paid	(383,000,000)	(449,000,000)	(425,000,000)
Total paid	(966,000,000)	(3,682,000,000)	(3,391,000,000)
Premium deficiency reserve	0	0	176,000,000
Balances at December 31	$ 101,000,000	$ 454,000,000	$ 741,000,000