Fair Value Measurements (Financial Assets and Liabilities Measured at Fair Value On a Recurring Basis) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Sep. 30, 2012 U.S. government and agency obligations [Member]	Sep. 30, 2013 Level 3 [Member] U.S. government and agency obligations [Member]	Sep. 30, 2013 Recurring [Member]	Mar. 31, 2013 Recurring [Member]	Sep. 30, 2013 Recurring [Member] Foreign currency swaps [Member]	Mar. 31, 2013 Recurring [Member] Foreign currency swaps [Member]	Sep. 30, 2013 Recurring [Member] Interest rate cap [Member]	Mar. 31, 2013 Recurring [Member] Interest rate cap [Member]	Sep. 30, 2013 Recurring [Member] Interest rate swap [Member]	Mar. 31, 2013 Recurring [Member] Interest rate swap [Member]	Sep. 30, 2013 Recurring [Member] Debt instruments [Member] U.S. government and agency obligations [Member]	Mar. 31, 2013 Recurring [Member] Debt instruments [Member] U.S. government and agency obligations [Member]	Sep. 30, 2013 Recurring [Member] Debt instruments [Member] Municipal debt securities [Member]	Mar. 31, 2013 Recurring [Member] Debt instruments [Member] Municipal debt securities [Member]	Sep. 30, 2013 Recurring [Member] Debt instruments [Member] Certificates Of Deposit [Member]	Mar. 31, 2013 Recurring [Member] Debt instruments [Member] Certificates Of Deposit [Member]	Sep. 30, 2013 Recurring [Member] Debt instruments [Member] Commercial paper [Member]	Mar. 31, 2013 Recurring [Member] Debt instruments [Member] Commercial paper [Member]	Sep. 30, 2013 Recurring [Member] Debt instruments [Member] Foreign government debt securities [Member]	Mar. 31, 2013 Recurring [Member] Debt instruments [Member] Foreign government debt securities [Member]	Sep. 30, 2013 Recurring [Member] Debt instruments [Member] Corporate debt securities [Member]	Mar. 31, 2013 Recurring [Member] Debt instruments [Member] Corporate debt securities [Member]	Sep. 30, 2013 Recurring [Member] Debt instruments [Member] U.S. government agency mortgage-backed securities [Member]	Mar. 31, 2013 Recurring [Member] Debt instruments [Member] U.S. government agency mortgage-backed securities [Member]	Sep. 30, 2013 Recurring [Member] Debt instruments [Member] Non-agency residential mortgage-backed securities [Member]	Mar. 31, 2013 Recurring [Member] Debt instruments [Member] Non-agency residential mortgage-backed securities [Member]	Sep. 30, 2013 Recurring [Member] Debt instruments [Member] Non-agency commercial mortgage-backed securities [Member]	Mar. 31, 2013 Recurring [Member] Debt instruments [Member] Non-agency commercial mortgage-backed securities [Member]	Sep. 30, 2013 Recurring [Member] Debt instruments [Member] Asset-backed securities [Member]	Mar. 31, 2013 Recurring [Member] Debt instruments [Member] Asset-backed securities [Member]	Sep. 30, 2013 Recurring [Member] Equity instruments [Member] Fixed income short-term sector fund [Member]	Mar. 31, 2013 Recurring [Member] Equity instruments [Member] Fixed income short-term sector fund [Member]	Sep. 30, 2013 Recurring [Member] Equity instruments [Member] Fixed income U.S. government sector fund [Member]	Mar. 31, 2013 Recurring [Member] Equity instruments [Member] Fixed income U.S. government sector fund [Member]	Sep. 30, 2013 Recurring [Member] Equity instruments [Member] Fixed income municipal sector fund [Member]	Mar. 31, 2013 Recurring [Member] Equity instruments [Member] Fixed income municipal sector fund [Member]	Sep. 30, 2013 Recurring [Member] Equity instruments [Member] Fixed income investment grade corporate sector fund [Member]	Mar. 31, 2013 Recurring [Member] Equity instruments [Member] Fixed income investment grade corporate sector fund [Member]	Sep. 30, 2013 Recurring [Member] Equity instruments [Member] Fixed income high-yield sector fund [Member]	Mar. 31, 2013 Recurring [Member] Equity instruments [Member] Fixed income high-yield sector fund [Member]	Sep. 30, 2013 Recurring [Member] Equity instruments [Member] Fixed income real return sector fund [Member]	Mar. 31, 2013 Recurring [Member] Equity instruments [Member] Fixed income real return sector fund [Member]	Sep. 30, 2013 Recurring [Member] Equity instruments [Member] Fixed income mortgage sector fund [Member]	Mar. 31, 2013 Recurring [Member] Equity instruments [Member] Fixed income mortgage sector fund [Member]	Sep. 30, 2013 Recurring [Member] Equity instruments [Member] Fixed income asset-backed securities sector fund [Member]	Mar. 31, 2013 Recurring [Member] Equity instruments [Member] Fixed income asset-backed securities sector fund [Member]	Sep. 30, 2013 Recurring [Member] Equity instruments [Member] Fixed income emerging market sector fund [Member]	Mar. 31, 2013 Recurring [Member] Equity instruments [Member] Fixed income emerging market sector fund [Member]	Sep. 30, 2013 Recurring [Member] Equity instruments [Member] Fixed income international sector fund [Member]	Mar. 31, 2013 Recurring [Member] Equity instruments [Member] Fixed income international sector fund [Member]	Sep. 30, 2013 Recurring [Member] Equity instruments [Member] Equity mutual fund - S&P 500 index [Member]	Mar. 31, 2013 Recurring [Member] Equity instruments [Member] Equity mutual fund - S&P 500 index [Member]	Sep. 30, 2013 Recurring [Member] Money market instruments [Member]	Mar. 31, 2013 Recurring [Member] Money market instruments [Member]	Sep. 30, 2013 Recurring [Member] Certificates of deposit [Member]	Mar. 31, 2013 Recurring [Member] Certificates of deposit [Member]	Sep. 30, 2013 Recurring [Member] Commercial paper [Member]	Mar. 31, 2013 Recurring [Member] Commercial paper [Member]	Sep. 30, 2013 Recurring [Member] Level 1 [Member]	Mar. 31, 2013 Recurring [Member] Level 1 [Member]	Sep. 30, 2013 Recurring [Member] Level 1 [Member] Foreign currency swaps [Member]	Mar. 31, 2013 Recurring [Member] Level 1 [Member] Foreign currency swaps [Member]	Sep. 30, 2013 Recurring [Member] Level 1 [Member] Interest rate cap [Member]	Mar. 31, 2013 Recurring [Member] Level 1 [Member] Interest rate cap [Member]	Sep. 30, 2013 Recurring [Member] Level 1 [Member] Interest rate swap [Member]	Mar. 31, 2013 Recurring [Member] Level 1 [Member] Interest rate swap [Member]	Sep. 30, 2013 Recurring [Member] Level 1 [Member] Debt instruments [Member] U.S. government and agency obligations [Member]	Mar. 31, 2013 Recurring [Member] Level 1 [Member] Debt instruments [Member] U.S. government and agency obligations [Member]	Sep. 30, 2013 Recurring [Member] Level 1 [Member] Debt instruments [Member] Municipal debt securities [Member]	Mar. 31, 2013 Recurring [Member] Level 1 [Member] Debt instruments [Member] Municipal debt securities [Member]	Sep. 30, 2013 Recurring [Member] Level 1 [Member] Debt instruments [Member] Certificates Of Deposit [Member]	Mar. 31, 2013 Recurring [Member] Level 1 [Member] Debt instruments [Member] Certificates Of Deposit [Member]	Sep. 30, 2013 Recurring [Member] Level 1 [Member] Debt instruments [Member] Commercial paper [Member]	Mar. 31, 2013 Recurring [Member] Level 1 [Member] Debt instruments [Member] Commercial paper [Member]	Sep. 30, 2013 Recurring [Member] Level 1 [Member] Debt instruments [Member] Foreign government debt securities [Member]	Mar. 31, 2013 Recurring [Member] Level 1 [Member] Debt instruments [Member] Foreign government debt securities [Member]	Sep. 30, 2013 Recurring [Member] Level 1 [Member] Debt instruments [Member] Corporate debt securities [Member]	Mar. 31, 2013 Recurring [Member] Level 1 [Member] Debt instruments [Member] Corporate debt securities [Member]	Sep. 30, 2013 Recurring [Member] Level 1 [Member] Debt instruments [Member] U.S. government agency mortgage-backed securities [Member]	Mar. 31, 2013 Recurring [Member] Level 1 [Member] Debt instruments [Member] U.S. government agency mortgage-backed securities [Member]	Sep. 30, 2013 Recurring [Member] Level 1 [Member] Debt instruments [Member] Non-agency residential mortgage-backed securities [Member]	Mar. 31, 2013 Recurring [Member] Level 1 [Member] Debt instruments [Member] Non-agency residential mortgage-backed securities [Member]	Sep. 30, 2013 Recurring [Member] Level 1 [Member] Debt instruments [Member] Non-agency commercial mortgage-backed securities [Member]	Mar. 31, 2013 Recurring [Member] Level 1 [Member] Debt instruments [Member] Non-agency commercial mortgage-backed securities [Member]	Sep. 30, 2013 Recurring [Member] Level 1 [Member] Debt instruments [Member] Asset-backed securities [Member]	Mar. 31, 2013 Recurring [Member] Level 1 [Member] Debt instruments [Member] Asset-backed securities [Member]	Sep. 30, 2013 Recurring [Member] Level 1 [Member] Equity instruments [Member] Fixed income short-term sector fund [Member]	Mar. 31, 2013 Recurring [Member] Level 1 [Member] Equity instruments [Member] Fixed income short-term sector fund [Member]	Sep. 30, 2013 Recurring [Member] Level 1 [Member] Equity instruments [Member] Fixed income U.S. government sector fund [Member]	Mar. 31, 2013 Recurring [Member] Level 1 [Member] Equity instruments [Member] Fixed income U.S. government sector fund [Member]	Sep. 30, 2013 Recurring [Member] Level 1 [Member] Equity instruments [Member] Fixed income municipal sector fund [Member]	Mar. 31, 2013 Recurring [Member] Level 1 [Member] Equity instruments [Member] Fixed income municipal sector fund [Member]	Sep. 30, 2013 Recurring [Member] Level 1 [Member] Equity instruments [Member] Fixed income investment grade corporate sector fund [Member]	Mar. 31, 2013 Recurring [Member] Level 1 [Member] Equity instruments [Member] Fixed income investment grade corporate sector fund [Member]	Sep. 30, 2013 Recurring [Member] Level 1 [Member] Equity instruments [Member] Fixed income high-yield sector fund [Member]	Mar. 31, 2013 Recurring [Member] Level 1 [Member] Equity instruments [Member] Fixed income high-yield sector fund [Member]	Sep. 30, 2013 Recurring [Member] Level 1 [Member] Equity instruments [Member] Fixed income real return sector fund [Member]	Mar. 31, 2013 Recurring [Member] Level 1 [Member] Equity instruments [Member] Fixed income real return sector fund [Member]	Sep. 30, 2013 Recurring [Member] Level 1 [Member] Equity instruments [Member] Fixed income mortgage sector fund [Member]	Mar. 31, 2013 Recurring [Member] Level 1 [Member] Equity instruments [Member] Fixed income mortgage sector fund [Member]	Sep. 30, 2013 Recurring [Member] Level 1 [Member] Equity instruments [Member] Fixed income asset-backed securities sector fund [Member]	Mar. 31, 2013 Recurring [Member] Level 1 [Member] Equity instruments [Member] Fixed income asset-backed securities sector fund [Member]	Sep. 30, 2013 Recurring [Member] Level 1 [Member] Equity instruments [Member] Fixed income emerging market sector fund [Member]	Mar. 31, 2013 Recurring [Member] Level 1 [Member] Equity instruments [Member] Fixed income emerging market sector fund [Member]	Sep. 30, 2013 Recurring [Member] Level 1 [Member] Equity instruments [Member] Fixed income international sector fund [Member]	Mar. 31, 2013 Recurring [Member] Level 1 [Member] Equity instruments [Member] Fixed income international sector fund [Member]	Sep. 30, 2013 Recurring [Member] Level 1 [Member] Equity instruments [Member] Equity mutual fund - S&P 500 index [Member]	Mar. 31, 2013 Recurring [Member] Level 1 [Member] Equity instruments [Member] Equity mutual fund - S&P 500 index [Member]	Sep. 30, 2013 Recurring [Member] Level 1 [Member] Money market instruments [Member]	Mar. 31, 2013 Recurring [Member] Level 1 [Member] Money market instruments [Member]	Sep. 30, 2013 Recurring [Member] Level 1 [Member] Certificates of deposit [Member]	Mar. 31, 2013 Recurring [Member] Level 1 [Member] Certificates of deposit [Member]	Sep. 30, 2013 Recurring [Member] Level 1 [Member] Commercial paper [Member]	Mar. 31, 2013 Recurring [Member] Level 1 [Member] Commercial paper [Member]	Sep. 30, 2013 Recurring [Member] Level 2 [Member]	Mar. 31, 2013 Recurring [Member] Level 2 [Member]	Sep. 30, 2013 Recurring [Member] Level 2 [Member] Foreign currency swaps [Member]	Mar. 31, 2013 Recurring [Member] Level 2 [Member] Foreign currency swaps [Member]	Sep. 30, 2013 Recurring [Member] Level 2 [Member] Interest rate cap [Member]	Mar. 31, 2013 Recurring [Member] Level 2 [Member] Interest rate cap [Member]	Sep. 30, 2013 Recurring [Member] Level 2 [Member] Interest rate swap [Member]	Mar. 31, 2013 Recurring [Member] Level 2 [Member] Interest rate swap [Member]	Sep. 30, 2013 Recurring [Member] Level 2 [Member] Debt instruments [Member] U.S. government and agency obligations [Member]	Mar. 31, 2013 Recurring [Member] Level 2 [Member] Debt instruments [Member] U.S. government and agency obligations [Member]	Sep. 30, 2013 Recurring [Member] Level 2 [Member] Debt instruments [Member] Municipal debt securities [Member]	Mar. 31, 2013 Recurring [Member] Level 2 [Member] Debt instruments [Member] Municipal debt securities [Member]	Sep. 30, 2013 Recurring [Member] Level 2 [Member] Debt instruments [Member] Certificates Of Deposit [Member]	Mar. 31, 2013 Recurring [Member] Level 2 [Member] Debt instruments [Member] Certificates Of Deposit [Member]	Sep. 30, 2013 Recurring [Member] Level 2 [Member] Debt instruments [Member] Commercial paper [Member]	Mar. 31, 2013 Recurring [Member] Level 2 [Member] Debt instruments [Member] Commercial paper [Member]	Sep. 30, 2013 Recurring [Member] Level 2 [Member] Debt instruments [Member] Foreign government debt securities [Member]	Mar. 31, 2013 Recurring [Member] Level 2 [Member] Debt instruments [Member] Foreign government debt securities [Member]	Sep. 30, 2013 Recurring [Member] Level 2 [Member] Debt instruments [Member] Corporate debt securities [Member]	Mar. 31, 2013 Recurring [Member] Level 2 [Member] Debt instruments [Member] Corporate debt securities [Member]	Sep. 30, 2013 Recurring [Member] Level 2 [Member] Debt instruments [Member] U.S. government agency mortgage-backed securities [Member]	Mar. 31, 2013 Recurring [Member] Level 2 [Member] Debt instruments [Member] U.S. government agency mortgage-backed securities [Member]	Sep. 30, 2013 Recurring [Member] Level 2 [Member] Debt instruments [Member] Non-agency residential mortgage-backed securities [Member]	Mar. 31, 2013 Recurring [Member] Level 2 [Member] Debt instruments [Member] Non-agency residential mortgage-backed securities [Member]	Sep. 30, 2013 Recurring [Member] Level 2 [Member] Debt instruments [Member] Non-agency commercial mortgage-backed securities [Member]	Mar. 31, 2013 Recurring [Member] Level 2 [Member] Debt instruments [Member] Non-agency commercial mortgage-backed securities [Member]	Sep. 30, 2013 Recurring [Member] Level 2 [Member] Debt instruments [Member] Asset-backed securities [Member]	Mar. 31, 2013 Recurring [Member] Level 2 [Member] Debt instruments [Member] Asset-backed securities [Member]	Sep. 30, 2013 Recurring [Member] Level 2 [Member] Equity instruments [Member] Fixed income short-term sector fund [Member]	Mar. 31, 2013 Recurring [Member] Level 2 [Member] Equity instruments [Member] Fixed income short-term sector fund [Member]	Sep. 30, 2013 Recurring [Member] Level 2 [Member] Equity instruments [Member] Fixed income U.S. government sector fund [Member]	Mar. 31, 2013 Recurring [Member] Level 2 [Member] Equity instruments [Member] Fixed income U.S. government sector fund [Member]	Sep. 30, 2013 Recurring [Member] Level 2 [Member] Equity instruments [Member] Fixed income municipal sector fund [Member]	Mar. 31, 2013 Recurring [Member] Level 2 [Member] Equity instruments [Member] Fixed income municipal sector fund [Member]	Sep. 30, 2013 Recurring [Member] Level 2 [Member] Equity instruments [Member] Fixed income investment grade corporate sector fund [Member]	Mar. 31, 2013 Recurring [Member] Level 2 [Member] Equity instruments [Member] Fixed income investment grade corporate sector fund [Member]	Sep. 30, 2013 Recurring [Member] Level 2 [Member] Equity instruments [Member] Fixed income high-yield sector fund [Member]	Mar. 31, 2013 Recurring [Member] Level 2 [Member] Equity instruments [Member] Fixed income high-yield sector fund [Member]	Sep. 30, 2013 Recurring [Member] Level 2 [Member] Equity instruments [Member] Fixed income real return sector fund [Member]	Mar. 31, 2013 Recurring [Member] Level 2 [Member] Equity instruments [Member] Fixed income real return sector fund [Member]	Sep. 30, 2013 Recurring [Member] Level 2 [Member] Equity instruments [Member] Fixed income mortgage sector fund [Member]	Mar. 31, 2013 Recurring [Member] Level 2 [Member] Equity instruments [Member] Fixed income mortgage sector fund [Member]	Sep. 30, 2013 Recurring [Member] Level 2 [Member] Equity instruments [Member] Fixed income asset-backed securities sector fund [Member]	Mar. 31, 2013 Recurring [Member] Level 2 [Member] Equity instruments [Member] Fixed income asset-backed securities sector fund [Member]	Sep. 30, 2013 Recurring [Member] Level 2 [Member] Equity instruments [Member] Fixed income emerging market sector fund [Member]	Mar. 31, 2013 Recurring [Member] Level 2 [Member] Equity instruments [Member] Fixed income emerging market sector fund [Member]	Sep. 30, 2013 Recurring [Member] Level 2 [Member] Equity instruments [Member] Fixed income international sector fund [Member]	Mar. 31, 2013 Recurring [Member] Level 2 [Member] Equity instruments [Member] Fixed income international sector fund [Member]	Sep. 30, 2013 Recurring [Member] Level 2 [Member] Equity instruments [Member] Equity mutual fund - S&P 500 index [Member]	Mar. 31, 2013 Recurring [Member] Level 2 [Member] Equity instruments [Member] Equity mutual fund - S&P 500 index [Member]	Sep. 30, 2013 Recurring [Member] Level 2 [Member] Money market instruments [Member]	Mar. 31, 2013 Recurring [Member] Level 2 [Member] Money market instruments [Member]	Sep. 30, 2013 Recurring [Member] Level 2 [Member] Certificates of deposit [Member]	Mar. 31, 2013 Recurring [Member] Level 2 [Member] Certificates of deposit [Member]	Sep. 30, 2013 Recurring [Member] Level 2 [Member] Commercial paper [Member]	Mar. 31, 2013 Recurring [Member] Level 2 [Member] Commercial paper [Member]	Sep. 30, 2013 Recurring [Member] Level 3 [Member]	Mar. 31, 2013 Recurring [Member] Level 3 [Member]	Sep. 30, 2013 Recurring [Member] Level 3 [Member] Foreign currency swaps [Member]	Mar. 31, 2013 Recurring [Member] Level 3 [Member] Foreign currency swaps [Member]	Sep. 30, 2013 Recurring [Member] Level 3 [Member] Interest rate cap [Member]	Mar. 31, 2013 Recurring [Member] Level 3 [Member] Interest rate cap [Member]	Sep. 30, 2013 Recurring [Member] Level 3 [Member] Interest rate swap [Member]	Mar. 31, 2013 Recurring [Member] Level 3 [Member] Interest rate swap [Member]	Sep. 30, 2013 Recurring [Member] Level 3 [Member] Debt instruments [Member] U.S. government and agency obligations [Member]	Mar. 31, 2013 Recurring [Member] Level 3 [Member] Debt instruments [Member] U.S. government and agency obligations [Member]	Sep. 30, 2013 Recurring [Member] Level 3 [Member] Debt instruments [Member] Municipal debt securities [Member]	Mar. 31, 2013 Recurring [Member] Level 3 [Member] Debt instruments [Member] Municipal debt securities [Member]	Sep. 30, 2013 Recurring [Member] Level 3 [Member] Debt instruments [Member] Certificates Of Deposit [Member]	Mar. 31, 2013 Recurring [Member] Level 3 [Member] Debt instruments [Member] Certificates Of Deposit [Member]	Sep. 30, 2013 Recurring [Member] Level 3 [Member] Debt instruments [Member] Commercial paper [Member]	Mar. 31, 2013 Recurring [Member] Level 3 [Member] Debt instruments [Member] Commercial paper [Member]	Sep. 30, 2013 Recurring [Member] Level 3 [Member] Debt instruments [Member] Foreign government debt securities [Member]	Mar. 31, 2013 Recurring [Member] Level 3 [Member] Debt instruments [Member] Foreign government debt securities [Member]	Sep. 30, 2013 Recurring [Member] Level 3 [Member] Debt instruments [Member] Corporate debt securities [Member]	Mar. 31, 2013 Recurring [Member] Level 3 [Member] Debt instruments [Member] Corporate debt securities [Member]	Sep. 30, 2013 Recurring [Member] Level 3 [Member] Debt instruments [Member] U.S. government agency mortgage-backed securities [Member]	Mar. 31, 2013 Recurring [Member] Level 3 [Member] Debt instruments [Member] U.S. government agency mortgage-backed securities [Member]	Sep. 30, 2013 Recurring [Member] Level 3 [Member] Debt instruments [Member] Non-agency residential mortgage-backed securities [Member]	Mar. 31, 2013 Recurring [Member] Level 3 [Member] Debt instruments [Member] Non-agency residential mortgage-backed securities [Member]	Sep. 30, 2013 Recurring [Member] Level 3 [Member] Debt instruments [Member] Non-agency commercial mortgage-backed securities [Member]	Mar. 31, 2013 Recurring [Member] Level 3 [Member] Debt instruments [Member] Non-agency commercial mortgage-backed securities [Member]	Sep. 30, 2013 Recurring [Member] Level 3 [Member] Debt instruments [Member] Asset-backed securities [Member]	Mar. 31, 2013 Recurring [Member] Level 3 [Member] Debt instruments [Member] Asset-backed securities [Member]	Sep. 30, 2013 Recurring [Member] Level 3 [Member] Equity instruments [Member] Fixed income short-term sector fund [Member]	Mar. 31, 2013 Recurring [Member] Level 3 [Member] Equity instruments [Member] Fixed income short-term sector fund [Member]	Sep. 30, 2013 Recurring [Member] Level 3 [Member] Equity instruments [Member] Fixed income U.S. government sector fund [Member]	Mar. 31, 2013 Recurring [Member] Level 3 [Member] Equity instruments [Member] Fixed income U.S. government sector fund [Member]	Sep. 30, 2013 Recurring [Member] Level 3 [Member] Equity instruments [Member] Fixed income municipal sector fund [Member]	Mar. 31, 2013 Recurring [Member] Level 3 [Member] Equity instruments [Member] Fixed income municipal sector fund [Member]	Sep. 30, 2013 Recurring [Member] Level 3 [Member] Equity instruments [Member] Fixed income investment grade corporate sector fund [Member]	Mar. 31, 2013 Recurring [Member] Level 3 [Member] Equity instruments [Member] Fixed income investment grade corporate sector fund [Member]	Sep. 30, 2013 Recurring [Member] Level 3 [Member] Equity instruments [Member] Fixed income high-yield sector fund [Member]	Mar. 31, 2013 Recurring [Member] Level 3 [Member] Equity instruments [Member] Fixed income high-yield sector fund [Member]	Sep. 30, 2013 Recurring [Member] Level 3 [Member] Equity instruments [Member] Fixed income real return sector fund [Member]	Mar. 31, 2013 Recurring [Member] Level 3 [Member] Equity instruments [Member] Fixed income real return sector fund [Member]	Sep. 30, 2013 Recurring [Member] Level 3 [Member] Equity instruments [Member] Fixed income mortgage sector fund [Member]	Mar. 31, 2013 Recurring [Member] Level 3 [Member] Equity instruments [Member] Fixed income mortgage sector fund [Member]	Sep. 30, 2013 Recurring [Member] Level 3 [Member] Equity instruments [Member] Fixed income asset-backed securities sector fund [Member]	Mar. 31, 2013 Recurring [Member] Level 3 [Member] Equity instruments [Member] Fixed income asset-backed securities sector fund [Member]	Sep. 30, 2013 Recurring [Member] Level 3 [Member] Equity instruments [Member] Fixed income emerging market sector fund [Member]	Mar. 31, 2013 Recurring [Member] Level 3 [Member] Equity instruments [Member] Fixed income emerging market sector fund [Member]	Sep. 30, 2013 Recurring [Member] Level 3 [Member] Equity instruments [Member] Fixed income international sector fund [Member]	Mar. 31, 2013 Recurring [Member] Level 3 [Member] Equity instruments [Member] Fixed income international sector fund [Member]	Sep. 30, 2013 Recurring [Member] Level 3 [Member] Equity instruments [Member] Equity mutual fund - S&P 500 index [Member]	Mar. 31, 2013 Recurring [Member] Level 3 [Member] Equity instruments [Member] Equity mutual fund - S&P 500 index [Member]	Sep. 30, 2013 Recurring [Member] Level 3 [Member] Money market instruments [Member]	Mar. 31, 2013 Recurring [Member] Level 3 [Member] Money market instruments [Member]	Sep. 30, 2013 Recurring [Member] Level 3 [Member] Certificates of deposit [Member]	Mar. 31, 2013 Recurring [Member] Level 3 [Member] Certificates of deposit [Member]	Sep. 30, 2013 Recurring [Member] Level 3 [Member] Commercial paper [Member]	Mar. 31, 2013 Recurring [Member] Level 3 [Member] Commercial paper [Member]	Sep. 30, 2013 Recurring [Member] Counterparty Netting & Collateral [Member]	Mar. 31, 2013 Recurring [Member] Counterparty Netting & Collateral [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents				$ 3,868	$ 4,251																																																	$ 2,595	$ 1,508	$ 1,270	$ 1,945	$ 3	$ 798	$ 2,152	$ 900																																																	$ 2,152	$ 900	$ 0	$ 0	$ 0	$ 0	$ 1,716	$ 3,351																																																	$ 443	$ 608	$ 1,270	$ 1,945	$ 3	$ 798	$ 0	$ 0																																																	$ 0	$ 0	$ 0	$ 0	$ 0	$ 0
Available-for-sale securities				4,364	5,397							105	104	14	16	1,412	2,041	202	495	3	3	137	128	74	87	5	5	49	51	19	13	43	43	321	312	21	22	305	327	42	42	273	293	559	648	48	47	64	66	169	170	499	484							545	526							46	42	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	499	484							3,742	4,798							57	62	14	16	1,412	2,041	202	495	3	3	135	124	74	87	0	0	0	0	0	0	43	43	321	312	21	22	305	327	42	42	273	293	559	648	48	47	64	66	169	170	0	0							77	73							2	0	0	0	0	0	0	0	0	0	2	4	0	0	5	5	49	51	19	13	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Derivative assets				62	58	951	1,139			406	580																																																	0	0	0	0			0	0																																																	1,280	1,644	887	1,076			393	568																																																	77	75	64	63			13	12																																																	(1,295)	(1,661)
Embedded derivative assets				0	0																																																							0	0																																																							0	0																																																							0	0
Total assets				8,294	9,706																																																							2,697	1,426																																																							6,738	9,793																																																							154	148																																																							(1,295)	(1,661)
Derivative liabilities				(1)	(5)	(164)	(131)	0	0	(688)	(766)																																																	0	0	0	0	0	0	0	0																																																	(838)	(889)	(150)	(123)	0	0	(688)	(766)																																																	(14)	(8)	(14)	(8)	0	0	0	0																																																	851	892
Embedded derivative liabilities				(9)	(12)																																																							0	0																																																							0	0																																																							(9)	(12)
Total liabilities				(10)	(17)																																																							0	0																																																							(838)	(889)																																																							(23)	(20)																																																							851	892
Total net assets				8,284	9,689																																																							2,697	1,426																																																							5,900	8,904																																																							131	128																																																							(444)	(769)
Transfers from Level 2 to Level 1	0	53
Reclassification from One Level 3 category to another			$ 2