Fair Value Measurements (Using Significant Unobservable Inputs) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value,	$ 162	$ 128
Gains/(losses) included in earnings	14	(18)
Gains/(losses) included in other comprehensive income	1	(3)
Purchases	4	7
Issuances	0	0
Sales	(2)	0
Settlements	(10)	(11)
Transfers in to Level 3	0	0
Transfers out of Level 3	0	0
Fair value,	169	103
The amount of total gains or (losses) for the period included in earnings attributable to the change in unrealized gains or losses related to assets still held at the reporting date	14	(21)
Available-for-sale securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value,	89	73
Gains/(losses) included in earnings	0	0
Gains/(losses) included in other comprehensive income	1	(3)
Purchases	4	7
Issuances	0	0
Sales	(2)	0
Settlements	(4)	(1)
Transfers in to Level 3	0	0
Transfers out of Level 3	0	0
Fair value,	88	76
U.S. government and agency obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value,	2
Gains/(losses) included in earnings	0
Gains/(losses) included in other comprehensive income	0
Purchases	0
Issuances	0
Sales	0
Settlements	0
Transfers in to Level 3	0
Transfers out of Level 3	0
Fair value,	2
Corporate debt securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value,	12	4
Gains/(losses) included in earnings	0	0
Gains/(losses) included in other comprehensive income	0	0
Purchases	0	0
Issuances	0	0
Sales	0	0
Settlements	0	0
Transfers in to Level 3	0	0
Transfers out of Level 3	0	0
Fair value,	12	4
Mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value,	48	56	[1]
Gains/(losses) included in earnings	0	0	[1]
Gains/(losses) included in other comprehensive income	1	(3)	[1]
Purchases	1	0	[1]
Issuances	0	0	[1]
Sales	(2)	0	[1]
Settlements	(3)	0	[1]
Transfers in to Level 3	0	0	[1]
Transfers out of Level 3	0	0	[1]
Fair value,	45	53	[1]
Asset-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value,	27	13
Gains/(losses) included in earnings	0	0
Gains/(losses) included in other comprehensive income	0	0
Purchases	3	7
Issuances	0	0
Sales	0	0
Settlements	(1)	(1)
Transfers in to Level 3	0	0
Transfers out of Level 3	0	0
Fair value,	29	19
Derivative [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value,	73	55
Gains/(losses) included in earnings	14	(18)
Gains/(losses) included in other comprehensive income	0	0
Purchases	0	0
Issuances	0	0
Sales	0	0
Settlements	(6)	(10)
Transfers in to Level 3	0	0
Transfers out of Level 3	0	0
Fair value,	81	27
The amount of total gains or (losses) for the period included in earnings attributable to the change in unrealized gains or losses related to assets still held at the reporting date	14	(21)
Interest rate swap [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value,	3	12
Gains/(losses) included in earnings	1	(1)
Gains/(losses) included in other comprehensive income	0	0
Purchases	0	0
Issuances	0	0
Sales	0	0
Settlements	(1)	0
Transfers in to Level 3	0	0
Transfers out of Level 3	0	0
Fair value,	3	11
The amount of total gains or (losses) for the period included in earnings attributable to the change in unrealized gains or losses related to assets still held at the reporting date	1	(1)
Foreign currency swaps [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value,	70	55
Gains/(losses) included in earnings	13	(22)
Gains/(losses) included in other comprehensive income	0	0
Purchases	0	0
Issuances	0	0
Sales	0	0
Settlements	(5)	(10)
Transfers in to Level 3	0	0
Transfers out of Level 3	0	0
Fair value,	78	23
The amount of total gains or (losses) for the period included in earnings attributable to the change in unrealized gains or losses related to assets still held at the reporting date	13	(19)
Embedded derivative liabilities, net
Fair Value Assets And Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Fair value,		(12)
Gains/(losses) included in earnings		5
Gains/(losses) included in other comprehensive income		0
Purchases		0
Issuances		0
Sales		0
Settlements		0
Transfers in to Level 3		0
Transfers out of Level 3		0
Fair value,		(7)
The amount of total gains or (losses) for the period included in earnings attributable to the change in unrealized gains or losses related to assets still held at the reporting date		$ (1)

[1] Certain prior period amounts have been reclassified to conform to the current year presentation.