Condensed Financial Information (Parent Company) (Basis of Presentation Income Statement) (Details) - USD ($) $ 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
Condensed Income Statements, Captions [Line Items]
Net Income (Loss) Available to Common Stockholders, Basic	$ 2,272	$ (97)	$ 865	$ 867	$ (2,388)	$ 536	$ 275	$ 2,324	$ 3,907	$ 747	$ 5,215
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									7,391	1,449	(574)
Net income (loss) attributable to MetLife, Inc.	2,317	(91)	911	873	(2,343)	542	321	2,330	4,010	850	5,373
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest									3,536	4,281	5,651
Revenues	15,840	16,171	15,333	14,964	12,387	15,806	16,349	16,245	62,308	60,787	61,343
Parent Company [Member]
Condensed Income Statements, Captions [Line Items]
Net Income (Loss) Available to Common Stockholders, Basic									3,907	747	5,215
Comprehensive Income (Loss), Net of Tax, Attributable to Parent									7,391	1,449	(574)
Net income (loss) attributable to MetLife, Inc.									4,010	850	5,373
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest									3,935	442	4,996
Revenues									5,994	2,131	6,347
Income (Loss) from Subsidiaries, before Tax									$ 7,162	1,833	6,048
Restatement Adjustment
Condensed Income Statements, Captions [Line Items]
Net Income (Loss) Available to Common Stockholders, Basic	181	(10)	27	47	(255)	(35)	211	129		50	63
Comprehensive Income (Loss), Net of Tax, Attributable to Parent										73	(6)
Net income (loss) attributable to MetLife, Inc.	181	(10)	27	47	(255)	(35)	211	129		50	63
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest										141	(57)
Revenues	86	67	47	39	(248)	(27)	324	148		197	9
Restatement Adjustment | Parent Company [Member]
Condensed Income Statements, Captions [Line Items]
Net Income (Loss) Available to Common Stockholders, Basic										50	63
Comprehensive Income (Loss), Net of Tax, Attributable to Parent										73	(6)
Net income (loss) attributable to MetLife, Inc.										50	63
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest										50	63
Revenues										50	63
Income (Loss) from Subsidiaries, before Tax										50	63
Scenario, Previously Reported
Condensed Income Statements, Captions [Line Items]
Net Income (Loss) Available to Common Stockholders, Basic	2,091	(87)	838	820	(2,133)	571	64	2,195		697	5,152
Comprehensive Income (Loss), Net of Tax, Attributable to Parent										1,376	(568)
Net income (loss) attributable to MetLife, Inc.	2,136	(81)	884	826	(2,088)	577	110	2,201		800	5,310
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest										4,140	5,708
Revenues	$ 15,754	$ 16,104	$ 15,286	$ 14,925	$ 12,635	$ 15,833	$ 16,025	$ 16,097		60,590	61,334
Scenario, Previously Reported | Parent Company [Member]
Condensed Income Statements, Captions [Line Items]
Net Income (Loss) Available to Common Stockholders, Basic										697	5,152
Comprehensive Income (Loss), Net of Tax, Attributable to Parent										1,376	(568)
Net income (loss) attributable to MetLife, Inc.										800	5,310
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest										392	4,933
Revenues										2,081	6,284
Income (Loss) from Subsidiaries, before Tax										$ 1,783	$ 5,985