Investments (Net Unrealized Investment Gains Losses) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Components of net unrealized investment gains (losses) included in accumulated other comprehensive income
Fixed maturity securities AFS	$ 44,415	$ 30,083	$ 11,381
Derivatives	1,924	2,209	2,127
Other	267	310	290
Subtotal	46,606	32,602	13,798
Future policy benefits	(7,828)	(1,019)	31
DAC, VOBA and DSI	(4,050)	(2,716)	(1,231)
Policyholder dividend obligation	(2,969)	(2,020)	(428)
Subtotal	(14,847)	(5,755)	(1,628)
Deferred income tax benefit (expense)	(8,009)	(6,850)	(3,505)
Net unrealized investment gains (losses)	23,750	19,997	8,665
Net unrealized investment gains (losses) attributable to noncontrolling interests	(20)	(16)	(10)
Net unrealized investment gains (losses) attributable to MetLife, Inc.	$ 23,730	$ 19,981	$ 8,655	$ 13,662