INVESTMENTS - Alternative Investment Funds (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Investments in Alternative Investment Funds
Alternative investment funds, unfunded commitments	$ 61	$ 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	1	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	145	152
Fair value | Private equity funds
Investments in Alternative Investment Funds
Non-marketable equity securities measured using the measurement alternative	123	123
Fair value | Real estate funds
Investments in Alternative Investment Funds
Non-marketable equity securities measured using the measurement alternative	2	9
Fair value | Mutual/collective investment funds
Investments in Alternative Investment Funds
Non-marketable equity securities measured using the measurement alternative	$ 20	$ 20