Variable Interest Entities and Other Investments (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012
Carrying amounts of assets liabilities and maximum exposure to loss related to unconsolidated variable interest entities
Unconsolidated VIEs, Total Assets	$ 840
Unconsolidated VIEs, Total Liabilities	42
Unconsolidated VIEs, Maximum Exposure to Loss	1,115
Low Income Housing Credit Investments [Member]
Carrying amounts of assets liabilities and maximum exposure to loss related to unconsolidated variable interest entities
Unconsolidated VIEs, Total Assets	541
Unconsolidated VIEs, Total Liabilities	42
Unconsolidated VIEs, Maximum Exposure to Loss	811
Renewable energy investments [Member]
Carrying amounts of assets liabilities and maximum exposure to loss related to unconsolidated variable interest entities
Unconsolidated VIEs, Total Assets	281
Unconsolidated VIEs, Total Liabilities	0
Unconsolidated VIEs, Maximum Exposure to Loss	281
Private Capital Investments [Member]
Carrying amounts of assets liabilities and maximum exposure to loss related to unconsolidated variable interest entities
Unconsolidated VIEs, Total Assets	18
Unconsolidated VIEs, Total Liabilities	0
Unconsolidated VIEs, Maximum Exposure to Loss	$ 23