Long-term and Short-term Debt (Credit Facilities) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Collateral financing arrangement	$ 1,121	$ 1,274
Committed Credit Facility Four [Member]
Debt Instrument [Line Items]
Borrowers	MetLife, Inc.
Expiration	Jun. 20, 2018
Line of Credit Facility, Maximum Borrowing Capacity	$ 395
Letters of Credit Issued	395
Collateral financing arrangement	0
Unused Commitments	$ 0
General Credit Facility Three [Member]
Debt Instrument [Line Items]
Borrowers	MetLife, Inc. and MetLife Funding, Inc.
Expiration	Dec. 20, 2021
Line of Credit Facility, Maximum Borrowing Capacity	$ 3,000
Letters of Credit Issued	130
Collateral financing arrangement	0
Unused Commitments	$ 2,870