Earnings Per Common Share (Earnings Per Common Share) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Weighted Average Shares:
Weighted average common stock outstanding for basic earnings per common share									1,069,700,000.0	1,100,500,000.0	1,117,800,000.0
Incremental common shares from assumed:
Incremental common shares from assumed exercise or issuance of stock-based awards					9,200,000.0				8,800,000.0	8,000,000	10,500,000.0
Weighted average common stock outstanding for diluted earnings per common share									1,078,500,000.0	1,108,500,000.0	1,128,300,000.0
Income (Loss) from Continuing Operations:
Income (loss) from continuing operations, net of income tax	$ 2,315	$ 883	$ 856	$ 952	$ (971)	$ 973	$ 1,686	$ 1,900	$ 5,006	$ 3,588	$ 4,061
Less: Income (loss) from continuing operations, net of income tax, attributable to noncontrolling interests									10	4	12
Less: Preferred stock dividends	$ 45	$ 6	$ 46	$ 6	$ 45	$ 6	$ 46	$ 6	103	103	116
Preferred stock repurchase premium									0	0	42
Income (loss) from continuing operations, net of income tax, available to MetLife, Inc.’s common shareholders									$ 4,893	$ 3,481	$ 3,891
Basic	$ 2.16	$ 0.82	$ 0.76	$ 0.87	$ (0.92)	$ 0.88	$ 1.49	$ 1.72	$ 4.57	$ 3.16	$ 3.48
Diluted	$ 2.14	$ 0.81	$ 0.75	$ 0.86	$ (0.92)	$ 0.87	$ 1.48	$ 1.71	$ 4.53	$ 3.13	$ 3.44
Income (Loss) from Discontinued Operations:
Income (loss) from discontinued operations, net of income tax	$ 0	$ (968)	$ 58	$ (76)	$ (1,370)	$ (435)	$ (1,361)	$ 432	$ (986)	$ (2,734)	$ 1,324
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									$ (986)	$ (2,734)	$ 1,324
Basic	$ 0.00	$ (0.91)	$ 0.05	$ (0.07)	$ (1.25)	$ (0.39)	$ (1.24)	$ 0.39	$ (0.92)	$ (2.48)	$ 1.19
Diluted	$ 0.00	$ (0.90)	$ 0.05	$ (0.07)	$ (1.25)	$ (0.39)	$ (1.23)	$ 0.39	$ (0.91)	$ (2.46)	$ 1.18
Net Income (Loss):
Net income (loss)	$ 2,315	$ (85)	$ 914	$ 876	$ (2,341)	$ 538	$ 325	$ 2,332	$ 4,020	$ 854	$ 5,385
Less: Net income (loss) attributable to noncontrolling interests	(2)	6	3	3	2	(4)	4	2	10	4	12
Less: Preferred stock dividends	45	6	46	6	45	6	46	6	103	103	116
Preferred stock repurchase premium									0	0	42
Net income (loss) available to MetLife, Inc.’s common shareholders	$ 2,272	$ (97)	$ 865	$ 867	$ (2,388)	$ 536	$ 275	$ 2,324	$ 3,907	$ 747	$ 5,215
Basic	$ 2.16	$ (0.09)	$ 0.81	$ 0.80	$ (2.17)	$ 0.49	$ 0.25	$ 2.11	$ 3.65	$ 0.68	$ 4.67
Diluted	$ 2.14	$ (0.09)	$ 0.80	$ 0.79	$ (2.17)	$ 0.48	$ 0.25	$ 2.10	$ 3.62	$ 0.67	$ 4.62