Investments (Changes in Net Unrealized Investment Gains Losses) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2021 USD ($)
Changes In Net Unrealized Investment Gains Losses Included In Accumulated Other Comprehensive Loss [Abstract]
Balance, beginning of period	$ 23,730
Unrealized investment gains (losses) during the period	(17,309)
Unrealized investment gains (losses) relating to:
Policyholder liabilities	6,808
DAC, VOBA and DSI	1,269
Deferred income tax benefit (expense)	2,215
Net unrealized investment gains (losses)	16,713
Net unrealized investment gains (losses) attributable to noncontrolling interests	(1)
Balance, end of period	16,712
Change in net unrealized investment gains (losses)	(7,017)
Change in net unrealized investment gains (losses) attributable to noncontrolling interests	(1)
Change in net unrealized investment gains (losses) attributable to MetLife, Inc.	$ (7,018)