INVESTMENTS - Alternative Investment Funds (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Investments in Alternative Investment Funds
Alternative investment funds, unfunded commitments	$ 62	$ 82
Private equity funds
Investments in Alternative Investment Funds
Alternative investment funds, unfunded commitments	60	62
Real estate funds
Investments in Alternative Investment Funds
Alternative investment funds, unfunded commitments	2	20
Mutual/collective investment funds
Investments in Alternative Investment Funds
Alternative investment funds, unfunded commitments	0	0
Fair value
Investments in Alternative Investment Funds
Non-marketable equity securities measured using the measurement alternative	139	152
Fair value | Private equity funds
Investments in Alternative Investment Funds
Non-marketable equity securities measured using the measurement alternative	116	123
Fair value | Real estate funds
Investments in Alternative Investment Funds
Non-marketable equity securities measured using the measurement alternative	4	9
Fair value | Mutual/collective investment funds
Investments in Alternative Investment Funds
Non-marketable equity securities measured using the measurement alternative	$ 19	$ 20