Investment Securities (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Schedule of Available for Sale Securities by Type
Cost	$ 4,992	$ 5,145
Gross Unrealized Gains	215	474
Gross Unrealized Losses	(70)	(5)
Estimated Fair Value	5,137	5,614
U.S. States and Political Subdivisions Debt Securities [Member]
Schedule of Available for Sale Securities by Type
Cost	4,197	4,280
Gross Unrealized Gains	63	199
Gross Unrealized Losses	(67)	(5)
Estimated Fair Value	4,193	4,474
U.S. Government agency obligations [Member]
Schedule of Available for Sale Securities by Type
Cost	3	3
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	3	3
U.S. Government treasury obligations [Member]
Schedule of Available for Sale Securities by Type
Cost	228	330
Gross Unrealized Gains	4	8
Gross Unrealized Losses	0	0
Estimated Fair Value	232	338
Corporate debt securities [Member]
Schedule of Available for Sale Securities by Type
Cost	42	73
Gross Unrealized Gains	3	6
Gross Unrealized Losses	0	0
Estimated Fair Value	45	79
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule of Available for Sale Securities by Type
Cost	170	210
Gross Unrealized Gains	7	14
Gross Unrealized Losses	0	0
Estimated Fair Value	177	224
Equity securities [Member]
Schedule of Available for Sale Securities by Type
Cost	37	64
Gross Unrealized Gains	131	232
Gross Unrealized Losses	0	0
Estimated Fair Value	168	296
Foreign government bonds and obligations [Member]
Schedule of Available for Sale Securities by Type
Cost	265	134
Gross Unrealized Gains	7	15
Gross Unrealized Losses	(1)	0
Estimated Fair Value	271	149
Availabe For Sale Securities Other [Member]
Schedule of Available for Sale Securities by Type
Cost	50	51
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(2)	0
Estimated Fair Value	$ 48	$ 51