Fair Values of Assets and Liabilities (Details 6) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Carrying Amount [Member]
Aggregate unpaid principal balance of MLHFS
Total Loans	$ 8,223	$ 6,925
Nonaccrual loans	9	10
Accruing loans 90 days or more past due	2	3
Aggregate Unpaid Principal [Member]
Aggregate unpaid principal balance of MLHFS
Total Loans	7,813	6,635
Nonaccrual loans	14	15
Accruing loans 90 days or more past due	2	4
Excess of Carrying Amount Over (Under) Unpaid Principal [Member]
Aggregate unpaid principal balance of MLHFS
Total Loans	410	290
Nonaccrual loans	(5)	(5)
Accruing loans 90 days or more past due	$ 0	$ (1)