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, 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
Weighted Average Shares:
Weighted average common stock outstanding - basic									937.6	1,005.9	1,069.7
Incremental common shares from assumed exercise or issuance of stock-based awards									6.8	8.0	8.8
Weighted average common stock outstanding - diluted									944.4	1,013.9	1,078.5
Income (Loss) from Continuing Operations:
Income (loss) from continuing operations, net of income tax									$ 5,909	$ 5,128	$ 5,006
Less: Income (loss) from continuing operations, net of income tax, attributable to noncontrolling interests									10	5	10
Less: Preferred stock dividends	$ 57	$ 32	$ 57	$ 32	$ 57	$ 32	$ 46	$ 6	178	141	103
Income (loss) from continuing operations, net of income tax, available to MetLife, Inc.’s common shareholders									$ 5,721	$ 4,982	$ 4,893
Basic									$ 6.10	$ 4.95	$ 4.57
Diluted									$ 6.06	$ 4.91	$ 4.53
Income (Loss) from Discontinued Operations:
Income (loss) from discontinued operations, net of income tax									$ 0	$ 0	$ (986)
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	$ 0	$ (986)
Basic									$ 0	$ 0	$ (0.92)
Diluted									$ 0	$ 0	$ (0.91)
Net Income (Loss):
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
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	$ 0.58	$ 2.31	$ 1.78	$ 1.41	$ 2.05	$ 0.89	$ 0.83	$ 1.20	$ 6.10	$ 4.95	$ 3.65
Diluted	$ 0.58	$ 2.30	$ 1.77	$ 1.40	$ 2.04	$ 0.88	$ 0.83	$ 1.19	$ 6.06	$ 4.91	$ 3.62