ALLIANCES - Financial Information Pertaining to Alliances (2seventy bio) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total Revenues		$ 45,006	$ 46,159	$ 46,385
Cost of products sold	[1]	10,693	10,137	9,940
Net product sales
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total Revenues		43,778	44,671	45,055
Alliance revenues
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total Revenues		13,151	12,743	11,556
Cost of products sold		6,067	5,768	5,227
Alliance revenues | Net product sales
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total Revenues		12,543	12,001	10,840
2seventy bio | Alliance revenues
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Cost of products sold		109	49	42
2seventy bio | Alliance revenues | Net product sales
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Total Revenues		$ 358	$ 297	$ 158

[1] Excludes amortization of acquired intangible assets.