Earnings Per Common Share (Earnings Per Common Share) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Weighted Average Shares:
Weighted average common stock outstanding - basic	873.3		908.8		879.3	911.5
Incremental common shares from assumed exercise or issuance of stock-based awards	6.4		4.3		6.5	5.0
Weighted average common stock outstanding - diluted	879.7		913.1		885.8	916.5
Net Income (Loss):
Net income (loss)	$ 3,412	$ 363	$ 150	$ 4,401	$ 3,775	$ 4,551
Less: Net income (loss) attributable to noncontrolling interests	5		5		10	8
Less: Preferred stock dividends	35	$ 68	77	$ 32	103	109
Preferred stock redemption premium	6		0		6	0
Net income (loss) available to MetLife, Inc.’s common shareholders	$ 3,366		$ 68		$ 3,656	$ 4,434
Basic	$ 3.85		$ 0.07		$ 4.16	$ 4.86
Diluted	$ 3.83		$ 0.07		$ 4.13	$ 4.84