Condensed Financial Information (Parent Company) (Basis of Presentation Cash Flow Statement) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Condensed Cash Flow Statements, Captions [Line Items]
Net income (loss) attributable to MetLife, Inc.	$ 2,317	$ (91)	$ 911	$ 873	$ (2,343)	$ 542	$ 321	$ 2,330	$ 4,010	$ 850	$ 5,373
Scenario, Previously Reported
Condensed Cash Flow Statements, Captions [Line Items]
Net income (loss) attributable to MetLife, Inc.	2,136	(81)	884	826	(2,088)	577	110	2,201		800	5,310
Restatement Adjustment
Condensed Cash Flow Statements, Captions [Line Items]
Net income (loss) attributable to MetLife, Inc.	$ 181	$ (10)	$ 27	$ 47	$ (255)	$ (35)	$ 211	$ 129		50	63
Parent Company [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net income (loss) attributable to MetLife, Inc.									4,010	850	5,373
Income (Loss) from Subsidiaries, before Tax									$ 7,162	1,833	6,048
Parent Company [Member] | Scenario, Previously Reported
Condensed Cash Flow Statements, Captions [Line Items]
Net income (loss) attributable to MetLife, Inc.										800	5,310
Income (Loss) from Subsidiaries, before Tax										1,783	5,985
Parent Company [Member] | Restatement Adjustment
Condensed Cash Flow Statements, Captions [Line Items]
Net income (loss) attributable to MetLife, Inc.										50	63
Income (Loss) from Subsidiaries, before Tax										$ 50	$ 63