Investments (Changes in Net Unrealized Investment Gains Losses) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2020 USD ($)
Changes In Net Unrealized Investment Gains Losses Included In Accumulated Other Comprehensive Loss [Abstract]
Balance, beginning of period	$ 19,981
Fixed maturity securities AFS on which noncredit OTTI losses have been recognized	(33)
Unrealized investment gains (losses) during the period	(1,512)
Unrealized investment gains (losses) relating to:
Future policy benefits	1,565
DAC, VOBA and DSI	(43)
Policyholder dividend obligation	343
Deferred income tax benefit (expense) related to noncredit OTTI losses recognized in AOCI	4
Deferred income tax benefit (expense)	65
Net unrealized investment gains (losses)	20,370
Net unrealized investment gains (losses) attributable to noncontrolling interests	(1)
Balance, end of period	20,369
Change in net unrealized investment gains (losses)	389
Change in net unrealized investment gains (losses) attributable to noncontrolling interests	(1)
Change in net unrealized investment gains (losses) attributable to MetLife, Inc.	$ 388