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NDT Funds (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract]
Amortized cost - maturity less than 1 year		$ 5
Amortized cost - maturity between 1 and 5 years		106
Amortized cost - maturity between 6 and 10 years		68
Amortized cost - maturity in excess of 10 years		54
Amortized cost total		233
Fair value - maturity less than 1 year		5
Fair value - maturity between 1 and 5 years		109
Fair value - maturity between 6 and 10 years		71
Fair value - maturity in excess of 10 years		60
Fair value total		245
Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract]
Proceeds from sales of NDT securities		54	$ 38
Gross realized gains	[1]	6	5
Gross realized losses	[1]	8	$ 3
NDT Funds
Available-for-sale Securities, Balance Sheet, Reported Amounts [Abstract]
Amortized cost		543		$ 538
Gross unrealized gains		421		413
Gross unrealized losses		0		0
Fair value		964		951
NDT Funds | Cash and cash equivalents
Available-for-sale Securities, Balance Sheet, Reported Amounts [Abstract]
Amortized cost		7		11
Gross unrealized gains		0		0
Gross unrealized losses		0		0
Fair value		7		11
NDT Funds | Equity securities
Available-for-sale Securities, Balance Sheet, Reported Amounts [Abstract]
Amortized cost		301		297
Gross unrealized gains		409		406
Gross unrealized losses		0		0
Fair value		710		703
NDT Funds | Debt securities
Available-for-sale Securities, Balance Sheet, Reported Amounts [Abstract]
Amortized cost		233		230
Gross unrealized gains		12		7
Gross unrealized losses		0		0
Fair value		245		237
NDT Funds | Receivables/payables, net
Available-for-sale Securities, Balance Sheet, Reported Amounts [Abstract]
Amortized cost		2		0
Gross unrealized gains		0		0
Gross unrealized losses		0		0
Fair value		$ 2		$ 0
[1] Excludes the impact of other-than-temporary impairment charges recognized on the Statements of Income.

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