Earnings Per Common Share (Earnings Per Common Share) (Details) - USD ($) $ / shares in Units, shares in Millions, $ 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
Weighted Average Shares:
Weighted average common stock outstanding for basic earnings per common share									1,005.9	1,069.7	1,100.5
Incremental common shares from assumed exercise or issuance of stock-based awards									8.0	8.8	8.0
Weighted average common stock outstanding for diluted earnings per common share									1,013.9	1,078.5	1,108.5
Income (Loss) from Continuing Operations:
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
Less: Income (loss) from continuing operations, net of income tax, attributable to noncontrolling interests									5	10	4
Less: Preferred stock dividends	$ 57	$ 32	$ 46	$ 6	$ 45	$ 6	$ 46	$ 6	141	103	103
Income (loss) from continuing operations, net of income tax, available to MetLife, Inc.’s common shareholders									$ 4,982	$ 4,893	$ 3,481
Basic	$ 2.05	$ 0.89	$ 0.83	$ 1.20	$ 2.16	$ 0.82	$ 0.76	$ 0.87	$ 4.95	$ 4.57	$ 3.16
Diluted	$ 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:
Income (loss) from discontinued operations, net of income tax	$ 0	$ 0	$ 0	$ 0	$ 0	$ (968)	$ 58	$ (76)	$ 0	$ (986)	$ (2,734)
Less: Income (loss) from discontinued operations, net of income tax, attributable to noncontrolling interests									0	0	0
Income (loss) from discontinued operations, net of income tax, available to MetLife, Inc.’s common shareholders									$ 0	$ (986)	$ (2,734)
Basic	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ 0.00	$ (0.91)	$ 0.05	$ (0.07)	$ 0.00	$ (0.92)	$ (2.48)
Diluted	$ 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):
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
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	$ 2.05	$ 0.89	$ 0.83	$ 1.20	$ 2.16	$ (0.09)	$ 0.81	$ 0.80	$ 4.95	$ 3.65	$ 0.68
Diluted	$ 2.04	$ 0.88	$ 0.83	$ 1.19	$ 2.14	$ (0.09)	$ 0.80	$ 0.79	$ 4.91	$ 3.62	$ 0.67