Earnings Per Common Share (Earnings Per Common Share) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Weighted Average Shares:
Weighted average common stock outstanding - basic	854.9	908.7			871.1	910.5
Incremental common shares from assumed exercise or issuance of stock-based awards	6.3	5.0			6.4	5.1
Weighted average common stock outstanding - diluted	861.2	913.7			877.5	915.6
Net Income (Loss):
Net income (loss)	$ 1,589	$ 709	$ 3,775	$ 4,551	$ 5,364	$ 5,260
Less: Net income (loss) attributable to noncontrolling interests	5	3			15	11
Less: Preferred stock dividends	63	59	103	$ 109	166	168
Preferred stock redemption premium	0	14	$ 6		6	14
Net income (loss) available to MetLife, Inc.’s common shareholders	$ 1,521	$ 633			$ 5,177	$ 5,067
Basic	$ 1.78	$ 0.70			$ 5.94	$ 5.57
Diluted	$ 1.77	$ 0.69			$ 5.90	$ 5.53