Investment Securities (Details 1) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Available-for-sale investment securities with gross unrealized losses and length of time
Estimated Fair Value, Less than 12 months	$ 509	$ 1,759
Estimated Fair Value, 12 months or more	132	123
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Gross Unrealized Losses, Less than 12 months	(15)	(67)
Gross Unrealized Losses, 12 months or more	(8)	(17)
U.S. States and Political Subdivisions Debt Securities [Member]
Available-for-sale investment securities with gross unrealized losses and length of time
Estimated Fair Value, Less than 12 months	351	1,320
Estimated Fair Value, 12 months or more	115	106
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Gross Unrealized Losses, Less than 12 months	(13)	(63)
Gross Unrealized Losses, 12 months or more	(7)	(16)
Foreign government bonds and obligations [Member]
Available-for-sale investment securities with gross unrealized losses and length of time
Estimated Fair Value, Less than 12 months	0	208
Estimated Fair Value, 12 months or more	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Gross Unrealized Losses, Less than 12 months	0	(1)
Gross Unrealized Losses, 12 months or more	0	0
U.S. Government agency obligations [Member]
Available-for-sale investment securities with gross unrealized losses and length of time
Estimated Fair Value, Less than 12 months	128	166
Estimated Fair Value, 12 months or more	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Gross Unrealized Losses, Less than 12 months	(1)	(1)
Gross Unrealized Losses, 12 months or more	0	0
Mortgage-backed securities [Member]
Available-for-sale investment securities with gross unrealized losses and length of time
Estimated Fair Value, Less than 12 months	0	35
Estimated Fair Value, 12 months or more	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Gross Unrealized Losses, Less than 12 months	0	(1)
Gross Unrealized Losses, 12 months or more	0	0
Other [Member]
Available-for-sale investment securities with gross unrealized losses and length of time
Estimated Fair Value, Less than 12 months	30	30
Estimated Fair Value, 12 months or more	17	17
Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract]
Gross Unrealized Losses, Less than 12 months	(1)	(1)
Gross Unrealized Losses, 12 months or more	$ (1)	$ (1)