Quarterly Results of Operations (Unaudited) (Quarterly Results of Operations) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 17,143	$ 18,678	$ 17,497	$ 16,302	$ 15,662	$ 16,289	$ 21,185	$ 14,805	$ 69,620	$ 67,941	$ 62,308
Total expenses	17,180	15,887	15,200	14,558	13,191	15,210	20,084	13,149	62,825	61,634	58,772
Net income (loss)	588	2,190	1,746	1,385	2,062	915	894	1,257	5,909	5,128	4,020
Less: Net income (loss) attributable to noncontrolling interests	(5)	6	5	4	(5)	3	3	4	10	5	10
Net income (loss) attributable to MetLife, Inc.	593	2,184	1,741	1,381	2,067	912	891	1,253	5,899	5,123	4,010
Less: Preferred stock dividends	57	32	57	32	57	32	46	6	178	141	103
Net income (loss) available to MetLife, Inc.’s common shareholders	$ 536	$ 2,152	$ 1,684	$ 1,349	$ 2,010	$ 880	$ 845	$ 1,247	$ 5,721	$ 4,982	$ 3,907
Basic earnings per common share
Net income (loss) attributable to MetLife, Inc.	$ 0.65	$ 2.35	$ 1.84	$ 1.44	$ 2.11	$ 0.92	$ 0.88	$ 1.21
Net income (loss) available to MetLife, Inc.’s common shareholders	0.58	2.31	1.78	1.41	2.05	0.89	0.83	1.20	$ 6.10	$ 4.95	$ 3.65
Diluted earnings per common share
Net income (loss) attributable to MetLife, Inc.	0.64	2.33	1.83	1.43	2.09	0.91	0.87	1.20
Net income (loss) available to MetLife, Inc.’s common shareholders	$ 0.58	$ 2.30	$ 1.77	$ 1.40	$ 2.04	$ 0.88	$ 0.83	$ 1.19	$ 6.06	$ 4.91	$ 3.62