RETIREMENT AND DEFERRED COMPENSATION PLANS - Fair Values of Plan Assets for Each Major Asset Category Based on Nature and Significant Concentration of Risks in Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 228	$ 208
Period for the portion of UK Equities, overseas equities, government bonds and corporate bonds, benchmarked against FTSE	5 years
Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 52	46
Overseas quoted equities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 52	46
Performance target over the benchmark	2.00%
Period for the portion of UK Equities, overseas equities, government bonds and corporate bonds, benchmarked against FTSE	3 years
Passive Global Equities
Defined Benefit Plan Disclosure [Line Items]
Portion of overseas equities	20.00%
Passive Global Equities Hedged
Defined Benefit Plan Disclosure [Line Items]
Portion of overseas equities	25.00%
Fundamental Indexation Global Equities
Defined Benefit Plan Disclosure [Line Items]
Portion of overseas equities	20.00%
Fundamental Indexation Global Equities Hedged
Defined Benefit Plan Disclosure [Line Items]
Portion of overseas equities	25.00%
Emerging Markets
Defined Benefit Plan Disclosure [Line Items]
Portion of overseas equities	10.00%
Debt securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 175	161
U.K. Government bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 140	129
Index - Linked Index
Defined Benefit Plan Disclosure [Line Items]
Portion of debt securities government bonds and corporate bonds benchmarked against FTSE	61.00%
Sterling Nominal LDI Bonds
Defined Benefit Plan Disclosure [Line Items]
Benchmarked against ILIM Custom Benchmark index	8.00%
Sterling Inflation Linked LDI Bonds
Defined Benefit Plan Disclosure [Line Items]
Benchmarked against ILIM Custom Benchmark index	31.00%
U.K. corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 35	32
Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 1	$ 1