Collateral Financing Arrangements (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2007
Collateral Financing Arrangements (Textuals) [Abstract]
Drawings upon the Collateral Financing Arrangement	$ 4,196,000,000	$ 4,647,000,000
Secured Debt [Member]
Collateral Financing Arrangements (Textuals) [Abstract]
Increase (Decrease) in Other Receivables	(59,000,000)	(84,000,000)
Partial repurchase	451,000,000	650,000,000
Parent Company [Member]
Collateral Financing Arrangements (Textuals) [Abstract]
Drawings upon the Collateral Financing Arrangement	2,797,000,000	2,797,000,000
Interest expense	985,000,000	1,007,000,000	882,000,000
MRC [Member] | Secured Debt [Member]
Collateral Financing Arrangements (Textuals) [Abstract]
Debt Instrument, Principal Outstanding	1,400,000,000	1,900,000,000
Debt Instrument, Term in Years				35 years
MRC [Member] | Secured Debt [Member]
Collateral Financing Arrangements (Textuals) [Abstract]
Partial repurchase	451,000,000	650,000,000
Debt Instrument, Face Amount				2,500,000,000
Debt Instrument, Interest Rate Terms				3-month LIBOR plus 0.55%
Debt Instrument, Basis Spread on Variable Rate				0.55%
Cash Collateral Returned, Net	0	100,000,000	0
Other Receivables	182,000,000	241,000,000
Invested assets pledged as collateral	120,000,000	125,000,000
Estimated fair value of assets held in trust	1,600,000,000	2,000,000,000
Interest expense	26,000,000	35,000,000	36,000,000
MRC [Member] | Parent Company [Member] | Secured Debt [Member]
Collateral Financing Arrangements (Textuals) [Abstract]
Debt Instrument, Interest Rate Terms				3-month LIBOR plus 1.12%
Debt Instrument, Basis Spread on Variable Rate				1.12%
MRSC [Member]
Collateral Financing Arrangements (Textuals) [Abstract]
Debt Instrument, Term in Years				30 years
MRSC [Member] | Secured Debt [Member]
Collateral Financing Arrangements (Textuals) [Abstract]
Statutory Reserve Support				3,500,000,000
Drawings upon the Collateral Financing Arrangement	2,800,000,000	2,800,000,000
Cash Collateral Paid	0	0	0
Cash Collateral Paid, Cumulative Net	680,000,000
Invested assets pledged as collateral	78,000,000	92,000,000
Estimated fair value of assets held in trust	3,400,000,000	3,300,000,000
Interest expense	$ 33,000,000	$ 29,000,000	$ 30,000,000
MRSC [Member] | Parent Company [Member] | Secured Debt [Member]
Collateral Financing Arrangements (Textuals) [Abstract]
Debt Instrument, Interest Rate Terms				3-month LIBOR plus 0.70
Debt Instrument, Basis Spread on Variable Rate				0.70%