EARNINGS PER SHARE (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share [Abstract]
Net (Loss)/Earnings Attributable to BMS	$ (10,027)	$ 1,872	$ (85)	$ (775)	$ (1,056)	$ 1,353	$ 1,432	$ 1,710	$ (9,015)	$ 3,439	$ 4,920
Weighted-average common shares outstanding - basic									2,258,000	1,705,000	1,633,000
Incremental shares attributable to share-based compensation plans									0	7,000	4,000
Weighted-average common shares outstanding - diluted									2,258,000	1,712,000	1,637,000
Earnings per Share - Basic	$ (4.45)	$ 0.83	$ (0.04)	$ (0.34)	$ (0.55)	$ 0.83	$ 0.88	$ 1.05	$ (3.99)	$ 2.02	$ 3.01
Earnings per Share - Diluted	$ (4.45)	$ 0.82	$ (0.04)	$ (0.34)	$ (0.55)	$ 0.83	$ 0.87	$ 1.04	$ (3.99)	$ 2.01	$ 3.01
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount									106,000