Quarterly Results of Operations (Unaudited) (Quarterly Results of Operations) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 15,662	$ 16,289	$ 21,185	$ 14,805	$ 15,840	$ 16,171	$ 15,333	$ 14,964	$ 67,941	$ 62,308	$ 60,787
Total expenses	13,191	15,210	20,084	13,149	14,879	15,686	14,315	13,892	61,634	58,772	56,506
Income (loss) from continuing operations, net of income tax	2,062	915	894	1,257	2,315	883	856	952	5,128	5,006	3,588
Income (loss) from discontinued operations, net of income tax	0	0	0	0	0	(968)	58	(76)	0	(986)	(2,734)
Net income (loss)	2,062	915	894	1,257	2,315	(85)	914	876	5,128	4,020	854
Less: Net income (loss) attributable to noncontrolling interests	(5)	3	3	4	(2)	6	3	3	5	10	4
Net income (loss) attributable to MetLife, Inc.	2,067	912	891	1,253	2,317	(91)	911	873	5,123	4,010	850
Less: Preferred stock dividends	57	32	46	6	45	6	46	6	141	103	103
Net income (loss) available to MetLife, Inc.’s common shareholders	$ 2,010	$ 880	$ 845	$ 1,247	$ 2,272	$ (97)	$ 865	$ 867	$ 4,982	$ 3,907	$ 747
Basic earnings per common share
Income (loss) from continuing operations, net of income tax, available to MetLife, Inc.’s common shareholders	$ 2.05	$ 0.89	$ 0.83	$ 1.20	$ 2.16	$ 0.82	$ 0.76	$ 0.87	$ 4.95	$ 4.57	$ 3.16
Income (loss) from discontinued operations, net of income tax, attributable to MetLife, Inc.	0.00	0.00	0.00	0.00	0.00	(0.91)	0.05	(0.07)	0.00	(0.92)	(2.48)
Net income (loss) attributable to MetLife, Inc.	2.11	0.92	0.88	1.21	2.20	(0.09)	0.86	0.80
Net income (loss) available to MetLife, Inc.’s common shareholders	2.05	0.89	0.83	1.20	2.16	(0.09)	0.81	0.80	4.95	3.65	0.68
Diluted earnings per common share
Income (loss) from continuing operations, net of income tax, available to MetLife, Inc.’s common shareholders	2.04	0.88	0.83	1.19	2.14	0.81	0.75	0.86	4.91	4.53	3.13
Income (loss) from discontinued operations, net of income tax, attributable to MetLife, Inc.	0.00	0.00	0.00	0.00	0.00	(0.90)	0.05	(0.07)	0.00	(0.91)	(2.46)
Net income (loss) attributable to MetLife, Inc.	2.09	0.91	0.87	1.20	2.18	(0.08)	0.85	0.79
Net income (loss) available to MetLife, Inc.’s common shareholders	$ 2.04	$ 0.88	$ 0.83	$ 1.19	$ 2.14	$ (0.09)	$ 0.80	$ 0.79	$ 4.91	$ 3.62	$ 0.67