Fair Value of Assets and Liabilities (Nonrecurring Fair Value Measurements) (Details) - Fair Value, Measurements, Nonrecurring - Level 3 - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Commercial mortgage loans
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value	$ 47	$ 0	$ 47	$ 0
Gains (Losses)	(2)	0	(6)	0
Mortgage servicing rights
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value	83	96	83	96
Gains (Losses)	0	(1)	(2)	(2)
Cost method investments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value	281	258	281	258
Gains (Losses)	$ (18)	$ (50)	$ (70)	$ (86)