Securities In An Unrealized Loss Position Securities In An Unrealized Loss Position (Narrative) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Number of securities	24
Preferred Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of securities	2
Available For Sale Equity Securities Non Investment Grade Continuous Unrealized Loss Position Aggregate Loss	0
Available For Sale Equity Securities Continuous Unrealized Loss Position Fair Value	25
Available For Sale Equity Securities Continuous Unrealized Loss Position Aggregate Loss	2
Common Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of securities	2
Available For Sale Equity Securities Continuous Unrealized Loss Position Fair Value	31
Available For Sale Equity Securities Continuous Unrealized Loss Position Aggregate Loss	1
External Credit Rating, Non Investment Grade [Member] | Preferred Stock [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of securities	1