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Fair Value Measurements Investments Gains (Losses) (Details) (USD $)	3 Months Ended		6 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Mar. 31, 2015	Mar. 31, 2014
Investment Gains (Losses)
Securities classified as trading and measured at fair value	$ 2,100,000,000us-gaap_TradingSecurities		$ 2,100,000,000us-gaap_TradingSecurities
NDT unfunded commitments related to private partnerships	103,000,000us-gaap_CommitmentsFairValueDisclosure		103,000,000us-gaap_CommitmentsFairValueDisclosure
SERP
Investment Gains (Losses)
Unrealized gains (losses) on investments	1,000,000	0	0	1,000,000
LTDCP [Member]
Investment Gains (Losses)
Unrealized gains (losses) on investments	0	0	(1,000,000)	0
NDT
Investment Gains (Losses)
Unrealized gains (losses) on investments	11,000,000	6,000,000	34,000,000	36,000,000
ART
Investment Gains (Losses)
Unrealized gains (losses) on investments	9,000,000	2,000,000	15,000,000	18,000,000
Maximum
Investment Gains (Losses)
Equity investments not required to be measured at fair value	$ 1,000,000		$ 1,000,000