Commitments and Contingencies (Impact of Adoption of Affordable Housing Guidance) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Dec. 31, 2014	Dec. 31, 2013
Commitments and Contingencies
Increase in other income	$ 34
Increase in provision for income taxes	(39)
Increase (decrease) in net income and net income available to common shareholders	(5)
Decrease in diluted EPS	$ (0.01)
Decrease in retained earnings		$ (49)	$ (29)