Investments (Net Unrealized Investment Gains Losses) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Components of net unrealized investment gains (losses) included in accumulated other comprehensive loss
Fixed maturity securities AFS	$ 11,381	$ 22,645
Fixed maturity securities AFS with noncredit OTTI losses included in AOCI	36	41
Total fixed maturity securities AFS	11,417	22,686
Equity securities	0	421
Derivatives	1,256	1,453
Other	85	46
Subtotal	12,758	24,606
Future policy benefits	(102)	(77)
DAC and VOBA related to noncredit OTTI losses recognized in AOCI	(1)	0
DAC, VOBA and DSI	(942)	(1,768)
Policyholder dividend obligation	(456)	(2,121)
Subtotal	(1,501)	(3,966)
Deferred income tax benefit (expense) related to noncredit OTTI losses recognized in AOCI	(5)	(12)
Deferred income tax benefit (expense)	(3,297)	(6,958)
Net unrealized investment gains (losses)	7,955	13,670
Net unrealized investment gains (losses) attributable to noncontrolling interests	(9)	(8)
Net unrealized investment gains (losses) attributable to MetLife, Inc.	$ 7,946	$ 13,662