Investments (Net Unrealized Investment Gains Losses) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Components of net unrealized investment gains (losses) included in accumulated other comprehensive loss
Fixed maturity securities	$ 22,645	$ 20,330	$ 18,158
Fixed maturity securities with noncredit OTTI losses included in AOCI	41	8	(76)
Total fixed maturity securities	22,686	20,338	18,082
Equity securities	421	485	422
Derivatives	1,453	2,923	2,350
Other	46	23	287
Subtotal	24,606	23,769	21,141
Future policy benefits	(77)	(1,114)	(163)
DAC and VOBA related to noncredit OTTI losses recognized in AOCI	0	(3)	0
DAC, VOBA and DSI	(1,768)	(1,430)	(1,273)
Policyholder dividend obligation	(2,121)	(1,931)	(1,783)
Subtotal	(3,966)	(4,478)	(3,219)
Deferred income tax benefit (expense) related to noncredit OTTI losses recognized in AOCI	(12)	(1)	27
Deferred income tax benefit (expense)	(6,958)	(6,634)	(6,149)
Net unrealized investment gains (losses)	13,670	12,656	11,800
Net unrealized investment gains (losses) attributable to noncontrolling interests	(8)	(6)	(31)
Net unrealized investment gains (losses) attributable to MetLife, Inc.	$ 13,662	12,650	11,769	$ 16,300
Net unrealized gains (losses) attributable to MetLife related to investments, derivatives , DAC, VOBA, DSI, and future policy benefits		$ 1,250	$ 1,554