Investments (Changes in Net Unrealized Investment Gains Losses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Changes In Net Unrealized Investment Gains Losses Included In Accumulated Other Comprehensive Loss [Abstract]
Balance at January 1,	$ 12,650	$ 11,769	$ 16,300
Fixed maturity securities on which noncredit OTTI losses have been recognized	33	84	36
Unrealized investment gains (losses) during the year	804	2,544	(11,668)
Unrealized investment gains (losses) relating to:
Future policy benefits	1,037	(951)	2,723
DAC and VOBA related to noncredit OTTI losses recognized in AOCI	3	(3)	4
DAC, VOBA and DSI	(338)	(157)	673
Policyholder dividend obligation	(190)	(148)	1,372
Deferred income tax benefit (expense) related to noncredit OTTI losses recognized in AOCI	(11)	(28)	(15)
Deferred income tax benefit (expense)	(324)	(485)	2,342
Net unrealized investment gains (losses)	13,664	12,625	11,767
Net unrealized investment gains (losses) attributable to noncontrolling interests	(2)	25	2
Balance at December 31,	13,662	12,650	11,769
Change in net unrealized investment gains (losses)	1,014	856	(4,533)
Change in net unrealized investment gains (losses) attributable to noncontrolling interests	(2)	25	2
Change in net unrealized investment gains (losses) attributable to MetLife, Inc.	$ 1,012	881	(4,531)
Changes in Net unrealized gains (losses) attributable to MetLife related to investments, derivatives, DAC, VOBA, DSI, and future policy benefits		$ (304)	$ (1,128)