Available-for-Sale Securities (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	$ 13,916	$ 12,714
Available-for-sale securities, gross unrealized gains	158	59
Available-for-sale securities, gross unrealized losses	(69)	(184)
Available-for-sale securities, fair value	14,005	12,589
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	13,883	12,681
Available-for-sale securities, gross unrealized gains	158	59
Available-for-sale securities, gross unrealized losses	(69)	(183)
Available-for-sale securities, fair value	13,972	12,557
Agency Mortgage-Backed Securities and CMOs [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	12,716	11,888
Available-for-sale securities, gross unrealized gains	106	41
Available-for-sale securities, gross unrealized losses	(63)	(166)
Available-for-sale securities, fair value	12,759	11,763
Agency Debentures [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	763	551
Available-for-sale securities, gross unrealized gains	42	18
Available-for-sale securities, gross unrealized losses	(1)	(12)
Available-for-sale securities, fair value	804	557
U.S. Treasuries [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	290	147
Available-for-sale securities, gross unrealized gains	7	0
Available-for-sale securities, gross unrealized losses	(4)	(4)
Available-for-sale securities, fair value	293	143
Agency Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	75	55
Available-for-sale securities, gross unrealized gains	2	0
Available-for-sale securities, gross unrealized losses	0	0
Available-for-sale securities, fair value	77	55
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	34	35
Available-for-sale securities, gross unrealized gains	1	0
Available-for-sale securities, gross unrealized losses	0	0
Available-for-sale securities, fair value	35	35
Corporate Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	5	5
Available-for-sale securities, gross unrealized losses	(1)	(1)
Available-for-sale securities, fair value	4	4
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities, amortized cost	33	33
Available-for-sale securities, gross unrealized losses	0	(1)
Available-for-sale securities, fair value	$ 33	$ 32

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
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=51813488&loc=d3e22054-111558

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 5
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27232-111563

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=49167202&loc=d3e26610-111562

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Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=27724398&loc=d3e27161-111563

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+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.2)
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