Investments (Changes in Net Unrealized Investment Gains Losses) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($)
Changes In Net Unrealized Investment Gains Losses Included In Accumulated Other Comprehensive Loss [Abstract]
Balance, beginning of period	$ 13,662
Changes In Net Unrealized Investment Gains Losses Related To Cumulative Effects Of Changes In Accounting Principles, Net Of Income Tax	1,258
Fixed maturity securities on which noncredit OTTI losses have been recognized	(6)
Unrealized investment gains (losses) during the period	(5,523)
Unrealized investment gains (losses) relating to:
Future policy benefits	(61)
DAC, VOBA and DSI	464
Policyholder dividend obligation	844
Deferred income tax benefit (expense) related to noncredit OTTI losses recognized in AOCI	7
Deferred income tax benefit (expense)	903
Net unrealized investment gains (losses)	11,548
Net unrealized investment gains (losses) attributable to noncontrolling interests	(1)
Balance, end of period	11,547
Change in net unrealized investment gains (losses)	(2,114)
Change in net unrealized investment gains (losses) attributable to noncontrolling interests	(1)
Change in net unrealized investment gains (losses) attributable to MetLife, Inc.	$ (2,115)