Liquidity Facilities and Letters of Credit (Details) (USD $) In Millions, unless otherwise specified	1 Months Ended
	Nov. 30, 2013	Jun. 30, 2014	Mar. 31, 2014
364 Day Credit Agreement Expiring 2015 [Member]
Line of Credit Facility [Line Items]
Initiation Date	Nov. 30, 2013
Maximum Borrowing Capacity	$ 4,300	$ 4,300
Credit facilities amount outstanding		0	0
Three Year Agreement Expiring 2017 [Member]
Line of Credit Facility [Line Items]
Initiation Date	Nov. 30, 2013
Maximum Borrowing Capacity	4,300	4,300
Credit facilities amount outstanding		0	0
Five Year Agreement Expiring 2019 [Member]
Line of Credit Facility [Line Items]
Initiation Date	Nov. 30, 2013
Maximum Borrowing Capacity	4,300	4,300
Credit facilities amount outstanding		0	0
Total Commited Bank Credit Facilities [Member]
Line of Credit Facility [Line Items]
Maximum Borrowing Capacity		6,000
Committed Bank Credit Facility Expiring 2015 [Member]
Line of Credit Facility [Line Items]
Maximum Borrowing Capacity		2,400
Credit facilities amount outstanding		0	0
Committed Bank Credit Facility Expiring 2016 [Member]
Line of Credit Facility [Line Items]
Maximum Borrowing Capacity		2,600
Credit facilities amount outstanding		0	0
Committed Bank Credit Facility Expiring 2017 [Member]
Line of Credit Facility [Line Items]
Maximum Borrowing Capacity		400
Credit facilities amount outstanding		0	0
Committed Bank Credit Facility Expiring 2018 [Member]
Line of Credit Facility [Line Items]
Maximum Borrowing Capacity		375
Credit facilities amount outstanding		0	0
Committed Bank Credit Facility Expiring 2020 [Member]
Line of Credit Facility [Line Items]
Maximum Borrowing Capacity		175
Credit facilities amount outstanding		$ 0	$ 0