Quarterly Results of Operations (Unaudited) (Quarterly Results of Operations) (Details) - USD ($) $ / shares in Units, $ 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
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 19,418	$ 16,015	$ 14,099	$ 18,310	$ 17,143	$ 18,678	$ 17,497	$ 16,302	$ 67,842	$ 69,620	$ 67,941
Total expenses	19,254	15,092	13,902	12,667	17,180	15,887	15,200	14,558	60,915	62,825	61,634
Net income (loss)	158	709	150	4,401	588	2,190	1,746	1,385	5,418	5,909	5,128
Less: Net income (loss) attributable to noncontrolling interests	0	3	5	3	(5)	6	5	4	11	10	5
Net income (loss) attributable to MetLife, Inc.	158	706	145	4,398	593	2,184	1,741	1,381	5,407	5,899	5,123
Less: Preferred stock dividends	34	59	77	32	57	32	57	32	202	178	141
Preferred stock redemption premium	0	14	0	0					14	0	0
Net income (loss) available to MetLife, Inc.’s common shareholders	$ 124	$ 633	$ 68	$ 4,366	$ 536	$ 2,152	$ 1,684	$ 1,349	$ 5,191	$ 5,721	$ 4,982
Basic earnings per common share
Net income (loss) attributable to MetLife, Inc.	$ 0.18	$ 0.78	$ 0.16	$ 4.81	$ 0.65	$ 2.35	$ 1.84	$ 1.44
Net income (loss) available to MetLife, Inc.’s common shareholders	0.14	0.70	0.07	4.78	0.58	2.31	1.78	1.41	$ 5.72	$ 6.10	$ 4.95
Diluted earnings per common share
Net income (loss) attributable to MetLife, Inc.	0.17	0.77	0.16	4.78	0.64	2.33	1.83	1.43
Net income (loss) available to MetLife, Inc.’s common shareholders	$ 0.14	$ 0.69	$ 0.07	$ 4.75	$ 0.58	$ 2.30	$ 1.77	$ 1.40	$ 5.68	$ 6.06	$ 4.91