Earnings Per Common Share (Earnings Per Common Share) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Weighted Average Shares:
Weighted average common stock outstanding for basic earnings per common share	1,035.9	1,090.4
Incremental common shares from assumed exercise or issuance of stock-based awards	8.5	8.3
Weighted average common stock outstanding for diluted earnings per common share	1,044.4	1,098.7
Income (Loss) from Continuing Operations:
Income (loss) from continuing operations, net of income tax	$ 1,257	$ 952
Less: Income (loss) from continuing operations, net of income tax, attributable to noncontrolling interests	4	3
Less: Preferred stock dividends	6	6
Income (loss) from continuing operations, net of income tax, available to MetLife, Inc.'s common shareholders	$ 1,247	$ 943
Basic	$ 1.20	$ 0.87
Diluted	$ 1.19	$ 0.86
Income (Loss) from Discontinued Operations:
Income (loss) from discontinued operations, net of income tax	$ 0	$ (76)
Less: Income (loss) from discontinued operations, net of income tax, attributable to noncontrolling interests	0	0
Income (loss) from discontinued operations, net of income tax, available to MetLife, Inc.’s common shareholders	$ 0	$ (76)
Basic	$ 0.00	$ (0.07)
Diluted	$ 0.00	$ (0.07)
Net Income (Loss):
Net income (loss)	$ 1,257	$ 876
Less: Net income (loss) attributable to noncontrolling interests	4	3
Less: Preferred stock dividends	6	6
Net income (loss) available to MetLife, Inc.’s common shareholders	$ 1,247	$ 867
Basic	$ 1.20	$ 0.80
Diluted	$ 1.19	$ 0.79