Quarterly Results of Operations (Unaudited) (Quarterly Results of Operations) (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
Quarterly Results of Operations (Unaudited)
Total revenues	$ 15,840	$ 16,171	$ 15,333	$ 14,964	$ 12,387	$ 15,806	$ 16,349	$ 16,245	$ 62,308	$ 60,787	$ 61,343
Total expenses	14,879	15,686	14,315	13,892	14,058	14,717	13,979	13,752	58,772	56,506	55,692
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
Income (loss) from discontinued operations, net of income tax	0	(968)	58	(76)	(1,370)	(435)	(1,361)	432	(986)	(2,734)	1,324
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
Net income (loss) attributable to MetLife, Inc.	2,317	(91)	911	873	(2,343)	542	321	2,330	4,010	850	5,373
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 earnings per common share
Income (loss) from continuing operations, net of income tax, available to MetLife, Inc.’s common shareholders	$ 2.16	$ 0.82	$ 0.76	$ 0.87	$ (0.92)	$ 0.88	$ 1.49	$ 1.72	$ 4.57	$ 3.16	$ 3.48
Income (loss) from discontinued operations, net of income tax, attributable to MetLife, Inc.	0.00	(0.91)	0.05	(0.07)	(1.25)	(0.39)	(1.24)	0.39	(0.92)	(2.48)	1.19
Net income (loss) attributable to MetLife, Inc.	2.20	(0.09)	0.86	0.80	(2.13)	0.49	0.29	2.12
Net income (loss) available to MetLife, Inc.’s common shareholders	2.16	(0.09)	0.81	0.80	(2.17)	0.49	0.25	2.11	3.65	0.68	4.67
Diluted earnings per common share
Income (loss) from continuing operations, net of income tax, available to MetLife, Inc.’s common shareholders	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, net of income tax, attributable to MetLife, Inc.	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) attributable to MetLife, Inc.	2.18	(0.08)	0.85	0.79	(2.13)	0.49	0.29	2.10
Net income (loss) available to MetLife, Inc.’s common shareholders	$ 2.14	$ (0.09)	$ 0.80	$ 0.79	$ (2.17)	$ 0.48	$ 0.25	$ 2.10	$ 3.62	$ 0.67	$ 4.62
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements					9,200,000.0				8,800,000.0	8,000,000	10,500,000.0
Scenario, Previously Reported
Quarterly Results of Operations (Unaudited)
Total revenues	$ 15,754	$ 16,104	$ 15,286	$ 14,925	$ 12,635	$ 15,833	$ 16,025	$ 16,097		$ 60,590	$ 61,334
Total expenses	14,879	15,603	14,309	13,921	14,017	14,674	13,979	13,780		56,450	55,626
Income (loss) from continuing operations, net of income tax	2,134	893	829	908	(795)	1,024	1,475	1,770		3,474	4,008
Income (loss) from discontinued operations, net of income tax	0	(968)	58	(79)	(1,291)	(451)	(1,361)	433		(2,670)	1,314
Net income (loss)	2,134	(75)	887	829	(2,086)	573	114	2,203		804	5,322
Less: Net income (loss) attributable to noncontrolling interests	(2)	6	3	3	2	(4)	4	2
Net income (loss) attributable to MetLife, Inc.	2,136	(81)	884	826	(2,088)	577	110	2,201		800	5,310
Less: Preferred stock dividends	45	6	46	6	45	6	46	6
Net income (loss) available to MetLife, Inc.’s common shareholders	$ 2,091	$ (87)	$ 838	$ 820	$ (2,133)	$ 571	$ 64	$ 2,195		$ 697	$ 5,152
Basic earnings per common share
Income (loss) from continuing operations, net of income tax, available to MetLife, Inc.’s common shareholders	$ 1.99	$ 0.83	$ 0.73	$ 0.82	$ (0.77)	$ 0.93	$ 1.30	$ 1.60		$ 3.06	$ 3.43
Income (loss) from discontinued operations, net of income tax, attributable to MetLife, Inc.	0.00	(0.91)	0.05	(0.07)	(1.17)	(0.41)	(1.24)	0.39
Net income (loss) attributable to MetLife, Inc.	2.03	(0.08)	0.82	0.76	(1.90)	0.52	0.10	2.00
Net income (loss) available to MetLife, Inc.’s common shareholders	1.99	(0.08)	0.78	0.75	(1.94)	0.52	0.06	1.99		0.63	4.61
Diluted earnings per common share
Income (loss) from continuing operations, net of income tax, available to MetLife, Inc.’s common shareholders	1.97	0.82	0.72	0.82	(0.77)	0.92	1.29	1.59		3.04	3.40
Income (loss) from discontinued operations, net of income tax, attributable to MetLife, Inc.	0.00	(0.90)	0.05	(0.07)	(1.17)	(0.41)	(1.23)	0.39
Net income (loss) attributable to MetLife, Inc.	2.01	(0.08)	0.82	0.75	(1.90)	0.52	0.10	1.99
Net income (loss) available to MetLife, Inc.’s common shareholders	$ 1.97	$ (0.08)	$ 0.77	$ 0.75	$ (1.94)	$ 0.51	$ 0.06	$ 1.98		$ 0.63	$ 4.57
Restatement Adjustment
Quarterly Results of Operations (Unaudited)
Total revenues	$ 86	$ 67	$ 47	$ 39	$ (248)	$ (27)	$ 324	$ 148		$ 197	$ 9
Total expenses	0	83	6	(29)	41	43	0	(28)		56	66
Income (loss) from continuing operations, net of income tax	181	(10)	27	44	(176)	(51)	211	130		114	53
Income (loss) from discontinued operations, net of income tax	0	0	0	3	(79)	16	0	(1)		(64)	10
Net income (loss)	181	(10)	27	47	(255)	(35)	211	129		50	63
Less: Net income (loss) attributable to noncontrolling interests	0	0	0	0	0	0	0	0
Net income (loss) attributable to MetLife, Inc.	181	(10)	27	47	(255)	(35)	211	129		50	63
Less: Preferred stock dividends	0	0	0	0	0	0	0	0
Net income (loss) available to MetLife, Inc.’s common shareholders	$ 181	$ (10)	$ 27	$ 47	$ (255)	$ (35)	$ 211	$ 129		$ 50	$ 63
Basic earnings per common share
Income (loss) from continuing operations, net of income tax, available to MetLife, Inc.’s common shareholders	$ 0.17	$ (0.01)	$ 0.03	$ 0.05	$ (0.15)	$ (0.05)	$ 0.19	$ 0.12		$ 0.10	$ 0.05
Income (loss) from discontinued operations, net of income tax, attributable to MetLife, Inc.	0.00	0.00	0.00	0.00	(0.08)	0.02	0.00	0.00
Net income (loss) attributable to MetLife, Inc.	0.17	(0.01)	0.04	0.04	(0.23)	(0.03)	0.19	0.12
Net income (loss) available to MetLife, Inc.’s common shareholders	0.17	(0.01)	0.03	0.05	(0.23)	(0.03)	0.19	0.12		0.05	0.06
Diluted earnings per common share
Income (loss) from continuing operations, net of income tax, available to MetLife, Inc.’s common shareholders	0.17	(0.01)	0.03	0.04	(0.15)	(0.05)	0.19	0.12		0.09	0.04
Income (loss) from discontinued operations, net of income tax, attributable to MetLife, Inc.	0.00	0.00	0.00	0.00	(0.08)	0.02	0.00	0.00
Net income (loss) attributable to MetLife, Inc.	0.17	0.00	0.03	0.04	(0.23)	(0.03)	0.19	0.11
Net income (loss) available to MetLife, Inc.’s common shareholders	$ 0.17	$ (0.01)	$ 0.03	$ 0.04	$ (0.23)	$ (0.03)	$ 0.19	$ 0.12		$ 0.04	$ 0.05