Investments (Securities In Unrealized Loss Positions Aggregated By Investment Category And Length Of Time In Loss Position) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	$ 12,231.0	$ 3,546.0
Less than 12 Months, Unrealized Loss	(51.0)	(10.0)
12 Months or More, Fair Value	16,873.0	35,898.0
12 Months Or More, Unrealized Loss	(349.0)	(691.0)
Total Fair Value	29,104.0	39,444.0
Total Unrealized Loss	(400.0)	(701.0)
U.S. Government-Sponsored Agency Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
12 Months or More, Fair Value		2,747.0
12 Months Or More, Unrealized Loss		(4.0)
Total Fair Value		2,747.0
Total Unrealized Loss		(4.0)
Obligations Of States And Political Subdivisions [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	2,736.0	857.0
Less than 12 Months, Unrealized Loss	(28.0)	(4.0)
12 Months or More, Fair Value	1,181.0	2,935.0
12 Months Or More, Unrealized Loss	(22.0)	(53.0)
Total Fair Value	3,917.0	3,792.0
Total Unrealized Loss	(50.0)	(57.0)
Mortgage-Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Less than 12 Months, Fair Value	9,495.0	2,689.0
Less than 12 Months, Unrealized Loss	(23.0)	(6.0)
12 Months or More, Fair Value	15,692.0	30,216.0
12 Months Or More, Unrealized Loss	(327.0)	(634.0)
Total Fair Value	25,187.0	32,905.0
Total Unrealized Loss	$ (350.0)	$ (640.0)