Earnings Per Common Share (Earnings Per Common Share) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Weighted Average Shares:
Weighted average common stock outstanding for basic earnings per common share	992.7	1,062.3	1,014.6	1,075.5
Incremental common shares from assumed exercise or issuance of stock-based awards	8.0	9.2	8.2	8.5
Weighted average common stock outstanding for diluted earnings per common share	1,000.7	1,071.5	1,022.8	1,084.0
Income (Loss) from Continuing Operations:
Income (loss) from continuing operations, net of income tax	$ 915	$ 883	$ 3,066	$ 2,691
Less: Income (loss) from continuing operations, net of income tax, attributable to noncontrolling interests	3	6	10	12
Less: Preferred stock dividends	32	6	84	58
Income (loss) from continuing operations, net of income tax, available to MetLife, Inc.'s common shareholders	$ 880	$ 871	$ 2,972	$ 2,621
Basic	$ 0.89	$ 0.82	$ 2.93	$ 2.44
Diluted	$ 0.88	$ 0.81	$ 2.91	$ 2.42
Income (Loss) from Discontinued Operations:
Income (loss) from discontinued operations, net of income tax	$ 0	$ (968)	$ 0	$ (986)
Less: Income (loss) from discontinued operations, net of income tax, attributable to noncontrolling interests	0	0	0	0
Income (loss) from discontinued operations, net of income tax, available to MetLife, Inc.’s common shareholders	$ 0	$ (968)	$ 0	$ (986)
Basic	$ 0.00	$ (0.91)	$ 0.00	$ (0.92)
Diluted	$ 0.00	$ (0.90)	$ 0.00	$ (0.91)
Net Income (Loss):
Net income (loss)	$ 915	$ (85)	$ 3,066	$ 1,705
Less: Net income (loss) attributable to noncontrolling interests	3	6	10	12
Less: Preferred stock dividends	32	6	84	58
Net income (loss) available to MetLife, Inc.’s common shareholders	$ 880	$ (97)	$ 2,972	$ 1,635
Basic	$ 0.89	$ (0.09)	$ 2.93	$ 1.52
Diluted	$ 0.88	$ (0.09)	$ 2.91	$ 1.51