Investments (Changes in Net Unrealized Investment Gains Losses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Changes In Net Unrealized Investment Gains Losses Included In Accumulated Other Comprehensive Loss [Abstract]
Balance at January 1,	$ 19,981	$ 8,655	$ 13,662
Cumulative effects of changes in accounting principles, net of income tax	0	21	1,258
Unrealized investment gains (losses) during the year	14,004	18,778	(10,383)
Unrealized investment gains (losses) relating to:
Future policy benefits	(6,809)	(1,050)	108
DAC, VOBA and DSI	(1,334)	(1,485)	537
Policyholder dividend obligation	(949)	(1,592)	1,693
Deferred income tax benefit (expense)	(1,159)	(3,340)	1,782
Net unrealized investment gains (losses)	23,734	19,987	8,657
Net unrealized investment gains (losses) attributable to noncontrolling interests	(4)	(6)	(2)
Balance at December 31,	23,730	19,981	8,655
Change in net unrealized investment gains (losses)	3,753	11,332	(5,005)
Change in net unrealized investment gains (losses) attributable to noncontrolling interests	(4)	(6)	(2)
Change in net unrealized investment gains (losses) attributable to MetLife, Inc.	$ 3,749	$ 11,326	$ (5,007)