Earnings Per Common Share (Earnings Per Common Share) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Weighted Average Shares:
Weighted average common stock outstanding - basic	885.4	914.1
Incremental common shares from assumed exercise or issuance of stock-based awards	6.7	5.9
Weighted average common stock outstanding - diluted	892.1	920.0
Net Income (Loss):
Net income (loss)	$ 363	$ 4,401
Less: Net income (loss) attributable to noncontrolling interests	5	3
Less: Preferred stock dividends	68	32
Net income (loss) available to MetLife, Inc.’s common shareholders	$ 290	$ 4,366
Basic	$ 0.33	$ 4.78
Diluted	$ 0.33	$ 4.75