Investment Securities (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2015	Dec. 31, 2014
Schedule of Available for Sale Securities by Type
Cost	$ 4,267	$ 4,280
Gross Unrealized Gains	152	154
Gross Unrealized Losses	(2)	(3)
Estimated Fair Value	4,417us-gaap_AvailableForSaleSecurities	4,431us-gaap_AvailableForSaleSecurities
U.S. States and Political Subdivisions Debt Securities [Member]
Schedule of Available for Sale Securities by Type
Cost	3,196	3,366
Gross Unrealized Gains	126	129
Gross Unrealized Losses	(1)	(2)
Estimated Fair Value	3,321	3,493
U.S. Government agency obligations [Member]
Schedule of Available for Sale Securities by Type
Cost	2	3
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Estimated Fair Value	2	3
U.S. Government treasury obligations [Member]
Schedule of Available for Sale Securities by Type
Cost	346	346
Gross Unrealized Gains	6	4
Gross Unrealized Losses	0	0
Estimated Fair Value	352	350
Corporate debt securities [Member]
Schedule of Available for Sale Securities by Type
Cost	35	37
Gross Unrealized Gains	2	3
Gross Unrealized Losses	0	0
Estimated Fair Value	37	40
Mortgage-backed securities [Member]
Schedule of Available for Sale Securities by Type
Cost	120	128
Gross Unrealized Gains	6	8
Gross Unrealized Losses	0	0
Estimated Fair Value	126	136
Equity securities [Member]
Schedule of Available for Sale Securities by Type
Cost	0	0
Gross Unrealized Gains	1	1
Gross Unrealized Losses	0	0
Estimated Fair Value	1	1
Foreign government bonds and obligations [Member]
Schedule of Available for Sale Securities by Type
Cost	518	350
Gross Unrealized Gains	11	9
Gross Unrealized Losses	0	0
Estimated Fair Value	529	359
Availabe For Sale Securities Other [Member]
Schedule of Available for Sale Securities by Type
Cost	50	50
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1)	(1)
Estimated Fair Value	$ 49	$ 49

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

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-Publisher FASB

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

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Amount of unrealized gain before deducting unrealized loss on investments in debt and equity securities classified as available-for-sale securities.

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Amount of unrealized loss before deducting unrealized gain on investments in available-for-sale securities.

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