Investments (Consolidated Variable Interest Entities) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Assets:
Accrued Investment Income Receivable	$ 575	$ 668
Liabilities
Long-term debt, at estimated fair value, relating to variable interest entities	46	1,904
Other liabilities relating to variable interest entities	4,419	5,445
MRSC (collateral financing arrangement) (1)
Assets:
Total assets	0	3,422
Consolidated securitization entities
Assets:
Mortgage loans (commercial mortgage loans)	115	136
Accrued Investment Income Receivable	1	1
Total assets	116	137
Liabilities
Long-term debt, at estimated fair value, relating to variable interest entities	11	23
Other liabilities relating to variable interest entities	0	1
Total liabilities	$ 11	$ 24