Earnings Per Common Share (Earnings Per Common Share) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Weighted Average Shares:
Weighted average common stock outstanding for basic earnings per common share	1,015.6	1,074.0	1,025.7	1,082.1
Incremental common shares from assumed exercise or issuance of stock-based awards	8.2	8.1	8.3	8.3
Weighted average common stock outstanding for diluted earnings per common share	1,023.8	1,082.1	1,034.0	1,090.4
Income (Loss) from Continuing Operations:
Income (loss) from continuing operations, net of income tax	$ 894	$ 856	$ 2,151	$ 1,808
Less: Income (loss) from continuing operations, net of income tax, attributable to noncontrolling interests	3	3	7	6
Less: Preferred stock dividends	46	46	52	52
Income (loss) from continuing operations, net of income tax, available to MetLife, Inc.'s common shareholders	$ 845	$ 807	$ 2,092	$ 1,750
Basic	$ 0.83	$ 0.76	$ 2.04	$ 1.62
Diluted	$ 0.83	$ 0.75	$ 2.02	$ 1.61
Income (Loss) from Discontinued Operations:
Income (loss) from discontinued operations, net of income tax	$ 0	$ 58	$ 0	$ (18)
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	$ 58	$ 0	$ (18)
Basic	$ 0.00	$ 0.05	$ 0.00	$ (0.02)
Diluted	$ 0.00	$ 0.05	$ 0.00	$ (0.02)
Net Income (Loss):
Net income (loss)	$ 894	$ 914	$ 2,151	$ 1,790
Less: Net income (loss) attributable to noncontrolling interests	3	3	7	6
Less: Preferred stock dividends	46	46	52	52
Net income (loss) available to MetLife, Inc.’s common shareholders	$ 845	$ 865	$ 2,092	$ 1,732
Basic	$ 0.83	$ 0.81	$ 2.04	$ 1.60
Diluted	$ 0.83	$ 0.80	$ 2.02	$ 1.59