Fair Value (Nonrecurring Fair Value Measurements) (Details) (Non recurring [Member], USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Real Estate Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value Prior to Measurement	$ 0	$ 0	$ 2	$ 5
Gain (Losses)	0	0	(1)	(3)
Real Estate Funds [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value After Measurement	0	0	1	2
Mortgage loans, net [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value Prior to Measurement	22	8	22	8
Gain (Losses)	(3)	4	(3)	4
Mortgage loans, net [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value After Measurement	19	12	19	12
Other limited partnership interests [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value Prior to Measurement	8	5	9	6
Gain (Losses)	(5)	(1)	(5)	(2)
Other limited partnership interests [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying Value After Measurement	$ 3	$ 4	$ 4	$ 4