Investments (Changes in Net Unrealized Investment Gains Losses) (Details) $ in Millions	9 Months Ended
	Sep. 30, 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	(13,026)
Unrealized investment gains (losses) relating to:
Policyholder liabilities	5,552
DAC, VOBA and DSI	776
Deferred income tax benefit (expense)	1,629
Net unrealized investment gains (losses)	18,661
Net unrealized investment gains (losses) attributable to noncontrolling interests	(3)
Balance, end of period	18,658
Change in net unrealized investment gains (losses)	(5,069)
Change in net unrealized investment gains (losses) attributable to noncontrolling interests	(3)
Change in net unrealized investment gains (losses) attributable to MetLife, Inc.	$ (5,072)