SIGNIFICANT ACCOUNTING POLICIES - ACCOUNTING AND CONSOLIDATION OF VIEs (Details) $ in Millions		Dec. 31, 2017 USD ($) joint_venture		Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Variable Interest Entity [Line Items]
Other equity investments		$ 1,351.0	[1]		$ 1,456.0	$ 1,440.0	$ 1,323.0	[1]
Number of consolidated real estate joint ventures | joint_venture		3
Number of non-consolidated real estate joint ventures | joint_venture		2
Total Assets		$ 225,985.0		$ 219,395.0	215,713.0	210,013.0	204,556.0
Real estate held for production of income	[1]	390.0					56.0
Total Liabilities		205,795.0		$ 202,815.0	$ 199,095.0	$ 195,091.0	189,549.0
Redeemable noncontrolling interest	[1]	626.0					403.0
Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Unfunded commitments		693.0
Real estate held for production of income		18.0					20.0
Variable Interest Entity, Not Primary Beneficiary | Other Equity Investments
Variable Interest Entity [Line Items]
Nonconsolidated VIE, carrying amount, assets		160,178.0
Maximum loss exposure, amount		1,123.0
Variable Interest Entity, Primary Beneficiary, Aggregated Disclosure
Variable Interest Entity [Line Items]
Total Assets		393.0					36.0
Real estate held for production of income		372.0					36.0
Total Liabilities		229.0					11.0
Long-term debt		203.0					$ 0.0
Individual Retirement | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Other equity investments		1,123.0
Protection Solutions | Variable Interest Entity, Not Primary Beneficiary
Variable Interest Entity [Line Items]
Nonconsolidated VIE, carrying amount, assets		53,600.0
Maximum loss exposure, amount		7.9
Voting Interest Entity, Primary Beneficiary, Aggregated Disclosure
Variable Interest Entity [Line Items]
Total Assets		58.0
Total Liabilities		2.0
Redeemable noncontrolling interest		$ 0.0
95% Owned
Variable Interest Entity [Line Items]
Number of consolidated real estate joint ventures | joint_venture		2
AB-Sponsored Investment Funds | Variable Interest Entity, Primary Beneficiary, Aggregated Disclosure
Variable Interest Entity [Line Items]
Total Assets		$ 1,550.0
Total Liabilities		696.0
Redeemable noncontrolling interest		$ 596.0

[1] See Note 2 for details of balances with variable interest entities.