Investments (Net Unrealized Investment Gains Losses) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Components of net unrealized investment gains (losses) included in accumulated other comprehensive loss
Fixed maturity securities that were temporarily impaired	$ 31,932	$ 33,641
Fixed maturity securities with noncredit OTTI losses in accumulated other comprehensive income (loss)	(260)	(361)	(724)
Total fixed maturity securities	31,672	33,280
Equity securities	341	97
Derivatives	1,393	1,274
Other	(16)	(30)
Subtotal	33,390	34,621
Insurance liability loss recognition	(5,613)	(6,049)
DAC and VOBA related to noncredit OTTI losses recognized in accumulated other comprehensive income (loss)	9	19
DAC and VOBA	(2,242)	(2,485)
Policyholder dividend obligation	(3,599)	(3,828)
Subtotal	(11,445)	(12,343)
Deferred income tax benefit (expense) related to noncredit OTTI losses recognized in accumulated other comprehensive income (loss)	87	119
Deferred income tax benefit (expense)	(7,788)	(7,973)
Net unrealized investment gains (losses)	14,244	14,424
Net unrealized investment gains (losses) attributable to noncontrolling interests	(7)	(5)
Net unrealized investment gains (losses) attributable to MetLife, Inc.	$ 14,237	$ 14,419